meson: don't use compiler.has_header

Meson's compiler.has_header is completely useless, it only checks that a
header exists, not whether it's usable. This creates problems if a
header contains a conditional #error declaration, like so:

> #if __x86_64__
> # error "Doesn't work with x86_64!"
> #endif

Compiler.has_header will return true in this case, even when compiling
for x86_64. This is useless.

Instead, we'll do a compile check so that any #error declarations will
be treated as errors, and compilation will work.

Fixes compilation on x32 architecture.

Gentoo Bugzilla: https://bugs.gentoo.org/show_bug.cgi?id=649746
meson bug: https://github.com/mesonbuild/meson/issues/2246
CC: Matt Turner <mattst88@gmail.com>
Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

meson.build

@@ -186,10 +186,10 @@ else
   dep_rt = []
 endif
 dep_m = cc.find_library('m', required : false)
-if cc.has_header('sys/sysctl.h')
+if cc.compiles('#include <sys/sysctl.h>', name : 'sys/sysctl.h works')
   config.set10('HAVE_SYS_SYSCTL_H', true)
 endif
-if cc.has_header('sys/select.h')
+if cc.compiles('#include <sys/select.h>', name : 'sys/select.h works')
   config.set10('HAVE_SYS_SELECT_H', true)
 endif
 if cc.has_header_symbol('sys/sysmacros.h', 'major')