https://sourceforge.net/p/vice-emu/patches/218/

Index: configure.ac
===================================================================
--- a/configure.ac	(revision 38502)
+++ b/configure.ac	(working copy)
@@ -1275,6 +1275,14 @@
   fi
 
   if test x"$found_sdl2" != "xyes"; then
+    PKG_CHECK_MODULES(SDL2, sdl2, [
+      use_sdl_prefix=no
+      use_sdl2_prefix=no
+      found_sdl2=yes
+      VICE_CFLAGS="$VICE_CFLAGS $SDL2_CFLAGS"
+      VICE_CXXFLAGS="$VICE_CXXFLAGS $SDL2_CFLAGS"
+      LIBS="$LIBS $SDL2_LIBS"
+    ], [
     dnl Check for sdl2-config
     if test x"$sdl2_config" != "xno"; then
       user_CFLAGS="$CFLAGS"
@@ -1311,6 +1319,7 @@
       CFLAGS="$user_CFLAGS"
       CXXFLAGS="$user_CXXFLAGS"
     fi
+    ])
   fi
 
   dnl fail if SDL2 ui was requested, otherwise restore flags and continue