Build with system clang

[riemass]

Currently only building within the LLVM project setup is possible. This is a tiresome process as LLVM builds for about 4 hours straight. I was able to build the tool using the system install of llvm/clang using the following compile flags:

clang++ reflect.cpp reflectedclass.cpp utils.cpp -I/usr/include/clang/Tooling/ -L/usr/lib/clang/9.0.0/lib/linux -lpthread -lclang -lclangAST -lclangASTMatchers -lclangTooling -lclangBasic -lclangFrontend -lclangSerialization -I/usr/include -std=c++11   -fno-exceptions -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -L/usr/lib -lLLVM-9

The llvm part of the output has been generated with the following command:

llvm-config --cxxflags --ldflags --ldflags 

This seems to be llvm's replacement for pkg-config.

However, the tool could not find any of the system headers. This is the output of a test run on a dummy file:

/usr/include/string.h:33:10: fatal error: 'stddef.h' file not found
#include <stddef.h>
a.out: ./classfinder.hpp:49: virtual void ClassFinder::onEndOfTranslationUnit(): Assertion `!ec && "error opening file"' failed.

I've tried using a compile_commands.json, and setting the paths manually using the --extra-arg switch, and both failed.
For this purpose, I should look into how other llvm/clang based tools, like ccls for example, have configured their CMakeLists.txt, as it can work with both, system library or the prepackaged release version of the library.