obsoleted - renamed to VL_PROG_CC_WARNINGS - or use AX_CFLAGS_WARN_ALL
Enables a reasonable set of warnings for the C compiler. Optionally,
if the first argument is nonempty, turns on flags which enforce and/or
enable proper ANSI C if such are known with the compiler used.
Currently this macro knows about GCC, Solaris C compiler,
Digital Unix C compiler, C for AIX Compiler, HP-UX C compiler,
IRIX C compiler, NEC SX-5 (Super-UX 10) C compiler, and Cray J90
(Unicos 10.0.0.8) C compiler.