sdl.m4: Call $PKG_CONFIG rather than hard-coding pkg-config

When cross-compiling, pkg.m4 will set the PKG_CONFIG variable
to a suitable pkg-config executable, which might be a
host-architecture-prefixed name like aarch64-linux-gnu-pkg-config. This
ensures that we will use a suitable search path that is suitable for
the host architecture (the machine we are compiling for) rather than
the build architecture (the machine we are compiling on) to find
dependency libraries like SDL. When using pkg-config as a substitute
for sdl2-config, we will similarly need to use the
host-architecture-prefixed pkg-config.

Setting the PKG_CONFIG environment variable is also the canonical way to
request that a different pkg-config implementation be used, if that
becomes necessary for some reason.

Co-authored-by: Helmut Grohne <[email protected]>
Bug-Debian: https://bugs.debian.org/1059749
Signed-off-by: Simon McVittie <[email protected]>

sdl.m4

@@ -5,7 +5,7 @@
 # stolen from Manish Singh
 # Shamelessly stolen from Owen Taylor
 
-# serial 2
+# serial 3
 
 dnl AM_PATH_SDL([MINIMUM-VERSION, [ACTION-IF-FOUND [, ACTION-IF-NOT-FOUND]]])
 dnl Test for SDL, and define SDL_CFLAGS and SDL_LIBS
@@ -45,7 +45,7 @@ AC_ARG_ENABLE(sdltest, [  --disable-sdltest       Do not try to compile and run
 
   if test "x$sdl_pc" = xyes ; then
     no_sdl=""
-    SDL_CONFIG="pkg-config sdl"
+    SDL_CONFIG="$PKG_CONFIG sdl"
   else
     as_save_PATH="$PATH"
     if test "x$prefix" != xNONE && test "$cross_compiling" != yes; then