mpg123: Fix compilation with clang.

mpg123: Fix compilation with clang.

clang -c -o libs/mpg123/src/compat/compat.cross.o ../wine.src/libs/mpg123/src/compat/compat.c -Ilibs/mpg123 \
  -I../wine.src/libs/mpg123 -Iinclude -I../wine.src/include -I../wine.src/include/msvcrt \
  -I../wine.src/libs/mpg123/src -I../wine.src/libs/mpg123/src/compat \
  -I../wine.src/libs/mpg123/src/libmpg123 -DOPT_GENERIC_DITHER -DREAL_IS_FLOAT -DNO_CATCHSIGNAL \
  -D_UCRT -D__WINE_PE_BUILD -target x86_64-windows -fno-strict-aliasing -Wno-pragma-pack -Wno-format \
  -mcx16 -gdwarf-2 -gstrict-dwarf -g -O2
In file included from ../wine.src/libs/mpg123/src/compat/compat.c:15:
../wine.src/libs/mpg123/src/compat/compat.h:74:10: fatal error: 'strings.h' file not found
         ^~~~~~~~~~~
1 error generated.
make: *** [Makefile:216382: libs/mpg123/src/compat/compat.cross.o] Error 1

Signed-off-by: Dmitry Timoshkov <dmitry@baikal.ru>
Signed-off-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>