Support both c++ standard libraries

[darkdragon-001]

I am using Ubuntu 21.04 with clang libc++-dev and iwyu package.

While I can build via

clang++ -stdlib=libc++ main.cpp

I cannot

include-what-you-use -stdlib=libc++ main.cpp

because of

In file included from main.cpp:1:
include/lib/lib.h:3:10: fatal error: 'string' file not found
#include <string>
         ^~~~~~~~

It resides in /usr/lib/llvm-11/include/c++/v1/. Adding -I/usr/lib/llvm-11/include/c++/v1 explicitly solves the problem. I think this should not be necessary as clang++ is capable of resolving it itself as well.

Might be related to #100

[kimgr]

I'm guessing include-what-you-use is not installed in the same directory as clang?

I think the Clang code IWYU uses bases its search path on the executable path (that's basically incorrect, but convenient), so if they're in different roots, well, it's not going to work.

[darkdragon-001]

Both are installed with prefix /usr as installed from Ubuntu repositories via apt. So they should have exactly the same executable path...

[kimgr]

What does which include-what-you-use and which clang (possibly with version suffix, e.g. clang-10) say on your system?

[darkdragon-001]

$ which clang
/usr/bin/clang
$ which include-what-you-use
/usr/bin/include-what-you-use

lrwxrwxrwx. 1 root root   24 Jan 14 15:39 /usr/bin/clang -> ../lib/llvm-11/bin/clang
lrwxrwxrwx. 1 root root   26 Jan 14 15:39 /usr/bin/clang++ -> ../lib/llvm-11/bin/clang++
lrwxrwxrwx. 1 root root   26 Jan  6 19:16 /usr/bin/clang++-11 -> ../lib/llvm-11/bin/clang++
lrwxrwxrwx. 1 root root   24 Jan  6 19:16 /usr/bin/clang-11 -> ../lib/llvm-11/bin/clang

[kimgr]

Could you try putting include-what-you-use in /usr/lib/llvm-11/bin/ and make the one in /usr/bin a symlink, like clang?

I'm curious if that "fixes" this, because then it's definitely a case of issue 100 again.