This file ends up included in
src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR3LibRuntimeXF86.cpp which
is compiled with -ffreestanding, so it shouldn't include math.h

See also: https://bugs.gentoo.org/907597

--- a/src/VBox/Additions/x11/x11include/XFree86-4.3/Xserver/misc.h
+++ b/src/VBox/Additions/x11/x11include/XFree86-4.3/Xserver/misc.h
@@ -169,6 +169,7 @@
 #ifndef IN_MODULE
 /* XXX Not for modules */
 #include <limits.h>
+#if defined __STDC_HOSTED__ && __STDC_HOSTED__ == 1
 #if !defined(MAXSHORT) || !defined(MINSHORT) || \
     !defined(MAXINT) || !defined(MININT)
 /*
@@ -178,6 +179,7 @@
 
 #include <math.h>
 #endif
+#endif	// defined __STDC_HOSTED__ && __STDC_HOSTED__ == 1
 #undef MAXSHORT
 #define MAXSHORT SHRT_MAX
 #undef MINSHORT