sim: bfin: move pkg-config & SDL checks to common code

This reduces the unique logic in bfin/configure to make it easier to
(eventually) unify it entirely.

sim/m4/sim_ac_platform.m4

@@ -162,4 +162,13 @@ AC_CHECK_LIB(socket, bind)
 AC_CHECK_LIB(nsl, gethostbyname)
 AC_CHECK_LIB(m, fabs)
 AC_CHECK_LIB(m, log2)
+
+PKG_CHECK_MODULES(SDL, sdl, [dnl
+  AC_CHECK_LIB(dl, dlopen, [dnl
+    SDL_CFLAGS="${SDL_CFLAGS} -DHAVE_SDL"
+    SDL_LIBS="-ldl"
+    ], [SDL_CFLAGS= SDL_LIBS=])
+  ], [:])
+AC_SUBST(SDL_CFLAGS)
+AC_SUBST(SDL_LIBS)
 ])

sim/m4/sim_ac_toolchain.m4

@@ -49,6 +49,7 @@ AC_SUBST(LDFLAGS_FOR_BUILD)
 AC_SUBST(CFLAGS)
 AC_CHECK_TOOL(AR, ar)
 AC_PROG_RANLIB
+PKG_PROG_PKG_CONFIG
 
 # Require C11 or newer.  Autoconf-2.70 provides ac_cv_prog_cc_c11 when using
 # AC_PROG_CC, but we're still using Autoconf-2.69, and the newest it understands