Merge #13445: build: Reset default -g -O2 flags when enable debug

9882d1f Reset default -g -O2 flags when enable debug (Chun Kuan Lee)

Pull request description:

  The default CXXFLAGS is -g -O2, this should not appear when enable debug.
  fixes #13432

Tree-SHA512: 79447f3e1fab9e6cd12f5ca49b3d42187e856e0c159ed01140ea93d6ef1fbb1af3d65b338308566330491052c0177d12abe26796513502ddde31692665a0dbb4

Author: laanwj

configure.ac

@@ -243,6 +243,10 @@ AC_LANG_PUSH([C++])
 AX_CHECK_COMPILE_FLAG([-Werror],[CXXFLAG_WERROR="-Werror"],[CXXFLAG_WERROR=""])
 
 if test "x$enable_debug" = xyes; then
+  # Clear default -g -O2 flags
+  if test "x$CXXFLAGS_overridden" = xno; then
+	CXXFLAGS=""
+  fi
   # Prefer -Og, fall back to -O0 if that is unavailable.
   AX_CHECK_COMPILE_FLAG(
     [-Og],