Add check for STDC_HEADERS. Should fix QNX 6.0 bustage.

Bug #107618

configure.in

@@ -915,7 +915,6 @@ case "$target" in
         AC_DEFINE(XP_OS2_VACPP)
         AC_DEFINE(TCPV40HDRS)
         AC_DEFINE(NSCAP_DISABLE_DEBUG_PTR_TYPES)
-        AC_DEFINE(STDC_HEADERS)
         MOZ_COMPONENT_NSPR_LIBS='$(NSPR_LIBS)'
         MKSHLIB='$(LD) $(DSO_LDOPTS)'
         MKCSHLIB='$(LD) $(DSO_LDOPTS)'
@@ -1296,6 +1295,7 @@ fi
 
 dnl Checks for header files.
 dnl ========================================================
+AC_HEADER_STDC
 AC_HEADER_DIRENT
 dnl -ldir is a noop for OS/2
 case "$target_os" in