machine/ieeefp.h: include <sys/cdefs.h>

[pkubaj]

Summary

The <machine/ieeefp.h> headers wrap their deprecated FPU control
interface prototypes (fpgetround() etc.) in BEGIN_DECLS/END_DECLS,
but rely on the includer to have pulled in <sys/cdefs.h>. On arm,
arm64, powerpc, and riscv, <floatingpoint.h> does not, so including it
as the very first header fails with "unknown type name BEGIN_DECLS".
On amd64, including <machine/ieeefp.h> directly with
IEEEFP_NOINLINES__ fails the same way. i386 does not use
__BEGIN_DECLS there.

This breaks e.g. devel/py-pyinstaller, whose bootloader main.c does

#ifdef __FreeBSD__
#include <floatingpoint.h>
#endif

as its first include.

Test Plan

Compiled a file containing only #include <floatingpoint.h> and one
containing only #include <machine/ieeefp.h>, as C and C++, with
cc -target <triple> -nostdinc -fsyntax-only against each architecture's
headers, for powerpc64, powerpc64le, armv7, aarch64, armv7 using the
arm64 headers (the arm path), riscv64, and amd64 with and without
-DIEEEFP_NOINLINES.

Before: 26 of 32 fail with "unknown type name 'BEGIN_DECLS'" (every
case except amd64 without IEEEFP_NOINLINES__ and amd64
<floatingpoint.h>). After: all 32 compile.

[jhb]

My suggestion would be to push the #include into the ieeefp.h headers themselves as they are the ones using __BEGIN_DECL.

[pkubaj]

Is that what you meant? Note that this now touches amd64 as well.