configure: Use -Wundef if supported by the compiler.

[Alexandre Julliard]

Gerald Pfeifer <gerald at pfeifer.com> writes:

> I verified this does not cause any warning on FreeBSD 8.1 test
> builds, and all the tools like bison and flex in somewhat current
> versions.

It's broken here with bison 2.4.1:

make[1]: Entering directory `/home/julliard/wine/wine/libs/wpp'
gcc -m32 -c -I. -I. -I../../include -I../../include   -D_REENTRANT -fPIC -Wall -pipe -fno-strict-aliasing -Wdeclaration-after-statement -Wstrict-prototypes -Wtype-limits -Wundef -Wwrite-strings -Wpointer-arith -Werror  -g -O2  -o ppy.tab.o ppy.tab.c
ppy.tab.c:336:6: error: "YYENABLE_NLS" is not defined
ppy.tab.c:910:6: error: "YYLTYPE_IS_TRIVIAL" is not defined
make[1]: *** [ppy.tab.o] Error 1

-- 
Alexandre Julliard
julliard at winehq.org