CONFIGURE: Add workaround for MinGW Win32 antivirus false positive on build.

This is triggered by the scummvm-conf.exe binary produced from the OpenGL test.

It is detected by a generic signature in AVG, Malware-bytes and several other
antivirus programs, so not easy to get this fixed.

This workaround avoids this by adding some redundant output code to the binary
which changes it enough to avoid the signature.

configure

@@ -3655,7 +3655,7 @@ if test "$_opengl" = auto ; then
 			# Test the current header for OpenGL
 			cat > $TMPC << EOF
 #include <$i>
-int main(void) { return GL_VERSION_1_1; }
+int main(void) { printf("ANTIVIRUS FALSE POSITIVE WORKAROUND"); return GL_VERSION_1_1; }
 EOF
 			cc_check $DEFINES $OPENGL_CFLAGS $OPENGL_LIBS && _opengl=yes && break