Avoid forcing -O3 and let users set these as wanted.
--- a/libretro/Makefile
+++ b/libretro/Makefile
@@ -579,6 +579,6 @@
    CXXFLAGS += -O2 -DNDEBUG
 else
-   CFLAGS += -O3 -DNDEBUG
-   CXXFLAGS += -O3 -DNDEBUG
+   CFLAGS += -DNDEBUG
+   CXXFLAGS += -DNDEBUG
 endif
 
--- a/unix/configure.ac
+++ b/unix/configure.ac
@@ -65,9 +65,4 @@
 	AC_S9X_COMPILER_FLAG([-g],  [g])
 	AC_S9X_COMPILER_FLAG([-O0], [o0])
-else
-	AC_S9X_COMPILER_FLAG([-O3], [o3], [
-		AC_S9X_COMPILER_FLAG([-O2], [o2], [
-			AC_S9X_COMPILER_FLAG([-O1], [o1])])])
-	AC_S9X_COMPILER_FLAG([-fomit-frame-pointer], [omit_frame_pointer])
 fi