sim: don't hardcode -ldl for SDL support

Since we use AC_SEARCH_LIBS to find dlopen, we don't need to hardcode
-ldl when using SDL ourselves.

sim/arch-subdir.mk.in

@@ -54,7 +54,6 @@ DEPMODE = @CCDEPMODE@
 DEPDIR = @DEPDIR@
 
 SDL_CFLAGS = @SDL_CFLAGS@
-SDL_LIBS = @SDL_LIBS@
 TERMCAP_LIB = @TERMCAP_LIB@
 READLINE_LIB = @READLINE_LIB@
 READLINE_CFLAGS = @READLINE_CFLAGS@

sim/bfin/Makefile.in

@@ -60,7 +60,6 @@ SIM_EXTRA_HW_DEVICES = \
 	eth_phy
 
 SIM_EXTRA_CFLAGS = $(SDL_CFLAGS)
-SIM_EXTRA_LIBS = $(SDL_LIBS)
 
 ## COMMON_POST_CONFIG_FRAG
 

sim/configure

@@ -13230,7 +13230,6 @@ else
         { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 	      SDL_CFLAGS="${SDL_CFLAGS} -DHAVE_SDL=1"
-      SDL_LIBS="-ldl"
 
 fi
 
@@ -13332,7 +13331,6 @@ else
         { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 	      SDL_CFLAGS="${SDL_CFLAGS} -DHAVE_SDL=1"
-      SDL_LIBS="-ldl"
 
 fi
 
@@ -13342,14 +13340,20 @@ else
         { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5
 $as_echo "yes" >&6; }
 	    SDL_CFLAGS="${SDL_CFLAGS} -DHAVE_SDL=2"
-    SDL_LIBS="-ldl"
+
+fi
+    if test -n "$SDL_CFLAGS"; then :
+      if test "$ac_cv_search_dlopen" = no; then :
+        { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: SDL support requires dlopen support" >&5
+$as_echo "$as_me: WARNING: SDL support requires dlopen support" >&2;}
+
+fi
 
 fi
 else
   SDL_CFLAGS=
-  SDL_LIBS=
 fi
-
+SDL_LIBS=
 
 
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for cygwin" >&5

sim/m4/sim_ac_platform.m4

@@ -154,19 +154,23 @@ AC_SEARCH_LIBS([dlopen], [dl])
 if test "${ac_cv_lib_dl_dlopen}" = "yes"; then
   PKG_CHECK_MODULES(SDL, sdl2, [dnl
     SDL_CFLAGS="${SDL_CFLAGS} -DHAVE_SDL=2"
-    SDL_LIBS="-ldl"
   ], [
     PKG_CHECK_MODULES(SDL, sdl, [dnl
       SDL_CFLAGS="${SDL_CFLAGS} -DHAVE_SDL=1"
-      SDL_LIBS="-ldl"
     ], [:])
   ])
+  dnl If we use SDL, we need dlopen support.
+  AS_IF([test -n "$SDL_CFLAGS"], [dnl
+    AS_IF([test "$ac_cv_search_dlopen" = no], [dnl
+      AC_MSG_WARN([SDL support requires dlopen support])
+    ])
+  ])
 else
   SDL_CFLAGS=
-  SDL_LIBS=
 fi
+dnl We dlopen the libs at runtime, so never pass down SDL_LIBS.
+SDL_LIBS=
 AC_SUBST(SDL_CFLAGS)
-AC_SUBST(SDL_LIBS)
 
 dnl In the Cygwin environment, we need some additional flags.
 AC_CACHE_CHECK([for cygwin], sim_cv_os_cygwin,