configure: improve tms470 compiler usage with glibc

Apply flags to work around glibc quirks only if glibc is detected,
and add a few more such flags.

Do not mess with as/ld settings in probe_cc.  This is not the
proper place.
Signed-off-by: Mans Rullgard <mans@mansr.com>

configure

@@ -2289,11 +2289,8 @@ probe_cc(){
         _type=tms470
         _ident=$($_cc -version | head -n1 | tr -s ' ')
         _flags='--gcc --abi=eabi -me'
-        _cflags='-D__gnuc_va_list=va_list -D__USER_LABEL_PREFIX__='
         _cc_e='-ppl -fe=$@'
         _cc_o='-fe=$@'
-        as_default="${cross_prefix}gcc"
-        ld_default="${cross_prefix}gcc"
         _depflags='-ppa -ppd=$(@:.o=.d)'
         _cflags_speed='-O3 -mf=5'
         _cflags_size='-O3 -mf=2'
@@ -2911,6 +2908,15 @@ fi
 
 test -n "$libc_type" && enable $libc_type
 
+# hacks for compiler/libc/os combinations
+
+if enabled_all tms470 glibc; then
+    add_cppflags -D__USER_LABEL_PREFIX__=
+    add_cppflags -D__builtin_memset=memset
+    add_cppflags -D__gnuc_va_list=va_list -D_VA_LIST_DEFINED
+    add_cflags   -pds=48    # incompatible redefinition of macro
+fi
+
 esc(){
     echo "$*" | sed 's/%/%25/g;s/:/%3a/g'
 }