float.h not found or included properly when using mingw-w64

Question

I'm trying to cross-compile a piece of code which uses float.h to set some FPU sizes.

The particular piece of code that requires it is:

#ifdef SINGLE
  _control87(_PC_24, _MCW_PC); /* Set FPU control word for single precision. */
#else /* not SINGLE */
  _control87(_PC_53, _MCW_PC); /* Set FPU control word for double precision. */
#endif /* not SINGLE */

When I compile, however, I get the error

/home/rcrozier/src/xfemm-hg/mfemm/../cfemm/fmesher/triangle.c:4922:14: error: '_PC_53' undeclared (first use in this function)
   _control87(_PC_53, _MCW_PC); /* Set FPU control word for double precision. */

Another person explains what seems to be the same problem in more detail here. There is also a very similar issue described in a (rather old) thread here. In case it's relevant, I'm using mingw-w64, but via the M Cross Environment

What exactly is the problem with float.h in this case, and is there a workaround?

EDIT: Verbose output from gcc

Using built-in specs.
COLLECT_GCC=/opt/mxe/usr/bin/x86_64-w64-mingw32.shared-gcc
Target: x86_64-w64-mingw32.shared
Configured with: /opt/mxe/tmp-gcc-x86_64-w64-mingw32.shared/gcc-4.9.4/configure --target=x86_64-w64-mingw32.shared --build=x86_64-unknown-linux-gnu --prefix=/opt/mxe/usr --libdir=/opt/mxe/usr/lib --enable-languages=c,c++,objc,fortran --enable-version-specific-runtime-libs --with-gcc --with-gnu-ld --with-gnu-as --disable-nls --disable-multilib --without-x --disable-win32-registry --enable-threads=win32 --enable-libgomp --with-gmp=/opt/mxe/usr/x86_64-unknown-linux-gnu --with-isl=/opt/mxe/usr/x86_64-unknown-linux-gnu --with-mpc=/opt/mxe/usr/x86_64-unknown-linux-gnu --with-mpfr=/opt/mxe/usr/x86_64-unknown-linux-gnu --with-cloog=/opt/mxe/usr/x86_64-unknown-linux-gnu --with-as=/opt/mxe/usr/bin/x86_64-w64-mingw32.shared-as --with-ld=/opt/mxe/usr/bin/x86_64-w64-mingw32.shared-ld --with-nm=/opt/mxe/usr/bin/x86_64-w64-mingw32.shared-nm
Thread model: win32
gcc version 4.9.4 (GCC) 
COLLECT_GCC_OPTIONS='-c' '-I' '../cfemm/fmesher' '-I' '../cfemm/libfemm' '-I' '../cfemm/libfemm/liblua' '-I' '/usr/local/MATLAB/R2015a/extern/include' '-I' '/usr/local/MATLAB/R2015a/simulink/include' '-D' 'MATLAB_MEX_FILE' '-std=c99' '-D' '_GNU_SOURCE' '-fexceptions' '-fPIC' '-fno-omit-frame-pointer' '-pthread' '-v' '-fpermissive' '-D' 'CPU86' '-D' 'MX_COMPAT_32' '-O' '-D' 'NDEBUG' '-o' '/home/rcrozier/src/xfemm-hg/mfemm/../cfemm/fmesher/triangle.o' '-mtune=generic' '-march=x86-64'
 /opt/mxe/usr/libexec/gcc/x86_64-w64-mingw32.shared/4.9.4/cc1 -quiet -v -I ../cfemm/fmesher -I ../cfemm/libfemm -I ../cfemm/libfemm/liblua -I /usr/local/MATLAB/R2015a/extern/include -I /usr/local/MATLAB/R2015a/simulink/include -D_REENTRANT -U_REENTRANT -D MATLAB_MEX_FILE -D _GNU_SOURCE -D CPU86 -D MX_COMPAT_32 -D NDEBUG /home/rcrozier/src/xfemm-hg/mfemm/../cfemm/fmesher/triangle.c -quiet -dumpbase triangle.c -mtune=generic -march=x86-64 -auxbase-strip /home/rcrozier/src/xfemm-hg/mfemm/../cfemm/fmesher/triangle.o -O -std=c99 -version -fexceptions -fPIC -fno-omit-frame-pointer -fpermissive -o /tmp/ccMkwwWD.s
cc1: warning: command line option '-fpermissive' is valid for C++/ObjC++ but not for C
GNU C (GCC) version 4.9.4 (x86_64-w64-mingw32.shared)
    compiled by GNU C version 4.8.4, GMP version 6.1.1, MPFR version 3.1.4, MPC version 1.0.2
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/opt/mxe/usr/lib/gcc/x86_64-w64-mingw32.shared/4.9.4/../../../../x86_64-w64-mingw32.shared/sys-include"
#include "..." search starts here:
#include <...> search starts here:
 ../cfemm/fmesher
 ../cfemm/libfemm
 ../cfemm/libfemm/liblua
 /usr/local/MATLAB/R2015a/extern/include
 /usr/local/MATLAB/R2015a/simulink/include
 /opt/mxe/usr/lib/gcc/x86_64-w64-mingw32.shared/4.9.4/include
 /opt/mxe/usr/lib/gcc/x86_64-w64-mingw32.shared/4.9.4/include-fixed
 /opt/mxe/usr/lib/gcc/x86_64-w64-mingw32.shared/4.9.4/../../../../x86_64-w64-mingw32.shared/include
End of search list.

EDIT: more info

I also get the same result if I use the full directory path to the mingw-w64 float.h like so:

//#include <float.h>
#include "/opt/mxe/usr/x86_64-w64-mingw32.static/include/float.h"

EDIT more info on code structure

To give some further information, I am actually compiling C library (header and C file) where declaration of the function I'm using is included using extern C. The actual declaration from the header file is shown below:

#ifdef __cplusplus
extern "C" {
#endif

#ifdef ANSI_DECLARATORS
int triangulate(char *, struct triangulateio *, struct triangulateio *,
                 struct triangulateio *, int (*TriMessage)(const char * format, ...));
void trifree(VOID *memptr);
#else /* not ANSI_DECLARATORS */
int triangulate();
void trifree();
#endif /* not ANSI_DECLARATORS */

#ifdef __cplusplus
}
#endif

The actual library I'm using is Triangle. The float.h include is in triangle.c, and looks like this:

#ifdef CPU86
//#include <float.h>
#include "/opt/mxe/usr/x86_64-w64-mingw32.static/include/float.h"
#endif /* CPU86 */
#ifdef LINUX
#include <fpu_control.h>
#endif /* LINUX */

Where you define CPU86 or LINUX at compile time. For the cross build, I'm defining CPU86.

Answer 1

OK, after some searching around I found this in triangle.c:

/* On some machines, my exact arithmetic routines might be defeated by the   */
/*   use of internal extended precision floating-point registers.  The best  */
/*   way to solve this problem is to set the floating-point registers to use */
/*   single or double precision internally.  On 80x86 processors, this may   */
/*   be accomplished by setting the CPU86 symbol for the Microsoft C         */
/*   compiler, or the LINUX symbol for the gcc compiler running on Linux.    */
/*                                                                           */

Note that it says "On 80x86 processors". The host you're compiling for - windows 64 bit (x86_64) - does not match that.

This is further supported by the official documentation from Microsoft about the extension that's used by the library you're trying to compile:

Mask

_MCW_PC (Precision control)

(Not supported on ARM or x64 platforms.)

[..]

_PC_24 (24 bits)

_PC_53 (53 bits)

_PC_64 (64 bits)

[..]

Thus I guess you need to configure your build differently, probably not defining CPU86. Though I don't know whether this really solves your issue, or just leads to wrong results. After all ... is this library even ported to 64 bit?