build: tms470: work around glibc math.h problems

The glibc definitions of INFINITY and NAN do not work with the
tms470 compiler, nor do our usual fallbacks.
Signed-off-by: Mans Rullgard <mans@mansr.com>

compat/tms470/math.h

+#include_next <math.h>
+
+#undef INFINITY
+#undef NAN
+
+#define INFINITY (*(const float*)((const unsigned []){ 0x7f800000 }))
+#define NAN      (*(const float*)((const unsigned []){ 0x7fc00000 }))

configure

@@ -2911,6 +2911,7 @@ test -n "$libc_type" && enable $libc_type
 # hacks for compiler/libc/os combinations
 
 if enabled_all tms470 glibc; then
+    CPPFLAGS="-I${source_path}/compat/tms470 ${CPPFLAGS}"
     add_cppflags -D__USER_LABEL_PREFIX__=
     add_cppflags -D__builtin_memset=memset
     add_cppflags -D__gnuc_va_list=va_list -D_VA_LIST_DEFINED