fix: add missing CXXFLAGS and CPPFLAGS to mp-build

mp-build/scripts/mp-build.sh

@@ -377,6 +377,8 @@ info "Running the build function"
 export CC="gcc"
 export CXX="g++"
 export CFLAGS="-march=x86-64 -mtune=generic -O2"
+export CPPFLAGS="-march=x86-64 -mtune=generic -O2"
+export CXXFLAGS="-march=x86-64 -mtune=generic -O2"
 export ROOTDIR="${rootpath}"
 export MAKEFLAGS="-j${OPT_CORES}"
 export MAKEOPTS="-j${OPT_CORES}"
@@ -396,6 +398,7 @@ fi
 
 unset XORG_CONFIG XORG_PREFIX
 unset MAKEOPTS MAKEFLAGS CXX
+unset CPPFLAGS CXXFLAGS
 unset CFLAGS ROOTDIR CC
 
 if [ "$SECONDS" != "0" ]; then