Disable strict aliasing

Harmonize C++ compiler flags with Node.js (-fno-rtti, -fno-exceptions)
and, critically, disable strict aliasing, because V8 is not the least
bit strict-aliasing safe.

Upstream turned it off in nodejs/node#54339,
like it always should have been, and I suspect the mismatch may be the
cause of segfaults that show up in production.

Remove -fpermissive, it's not needed and something to discourage.

ext/mini_racer_extension/extconf.rb

@@ -18,7 +18,9 @@
 $CXXFLAGS += " -rdynamic" unless $CXXFLAGS.split.include? "-rdynamic"
 $CXXFLAGS += " -fPIC" unless $CXXFLAGS.split.include? "-rdynamic" or IS_DARWIN
 $CXXFLAGS += " -std=c++17"
-$CXXFLAGS += " -fpermissive"
+$CXXFLAGS += " -fno-rtti"
+$CXXFLAGS += " -fno-exceptions"
+$CXXFLAGS += " -fno-strict-aliasing"
 #$CXXFLAGS += " -DV8_COMPRESS_POINTERS"
 $CXXFLAGS += " -fvisibility=hidden "