Infer resource dir from tool executable path

[envp]

Internal ticket ID ENG2STAAR-1699

Describe your changes This change fixes the following bug in all tools built using clangmetatool::ToolApplicationSupport:

If the compiler appearing the compilation database is not clang or doesn't have an installation of clangmetatool at a predefined location, we would need to provide -resource-dir as an extra argument to allow it to detect where standard C/C++ headers such as stdarg.h, stddef.h, or iostream lived.

Tools built, and installed using clangmetatool will now be able to infer the location of clang's bundled standard includes automatically, if they are conventionally installed with clangmetatool_install(...). This change will continue to support passing -resource-dir to override this automatic detection.

This is enabled by:

• Letting the executables inform clangmetatool of the 'main' function that is used to detect the binary name, and we assume that a resource directory exists relative to this (since clangmetatool_install ensures this)
• If the first step fails to locate an executable, then we attempt to find the basename in $PATH

Signed-off-by: Vaibhav Yenamandra vyenamandra@bloomberg.net

Testing performed

• LLVM-8 / Darwin 18.6.0
• docker with LLVM-7 / ubuntu:18.04
• docker with LLVM-8 / ubuntu:18.10
• docker with LLVM-9 / ubuntu:19.04

Additional context Internally reported bugfix, current workaround is for tools to specificy -resource-dir or --gcc-toolchain as hints to find standard include dirs.

[envp]

cc: @dbeer1 @HaltCatchFire

[dbeer1]

CI seems to fail