build: Remove LLVM_(CPPFLAGS|CXXFLAGS) from XTRA_CXXFLAGS. * configure.ac: Don't add LLVM_CPPFLAGS, LLVM_CXXFLAGS to XTRA_CXXFLAGS. * libinterp/Makefile.am: Add LLVM_CPPFLAGS to *.cc -> *.df rule. * libinterp/corefcn/module.mk: Add LLVM_CPPFLAGS to corefcn specific CPPFLAGS. Create new corefcn specific CXXFLAGS variable and add LLVM_CXXFLAGS to it.

# u_vr.m

## define and exectute "__demo__" once
eval ("function __demo__ ();  df_vr;  v = vr * 2; endfunction");
__demo__;

## clear definition of "__demo__"
clear __demo__

## define and exectute "__demo__" once more
eval ("function __demo__ ();  df_vr;  v = vr * 2; endfunction");
__demo__;