mingw-w64-x86_64-clang: can not build with coverage info.

[LebedevRI]

I compile with -fprofile-arcs -ftest-coverage flags, and link with -fprofile-arcs -ftest-coverage --coverage flags, as stated everywhere.
On my local machine, with debian sid + clang 3.9 / 4.0 it does work, and the resulting binary does produce coverage data.
On appveyor ci, with msys2 + mingw-w64-x86_64-clang, linking step fails with messages like undefined reference to llvm_gcda_start_file'`" and so on.

Packages i install manually: mingw-w64-x86_64-{toolchain,gcc,clang,cmake,ninja,libxml2,pugixml,libjpeg-turbo,zlib}

What other information can i provide?

[mati865]

I worry one could say:

It's not a bug, it's a feature.

Feature reserved for UNIX like systems: in ToolChains.cpp there are void Darwin::addProfileRTLibs(...) and void Linux::addProfileRTLibs(...) functions but nothing like Windows.
Those functions add aguments to the linker so it can link GCOV/GCDA symbols.

Also MSVC Clang either dumps core or cannot link symbols (depends on tested code):

clang_rt.profile-x86_64.lib(GCDAProfiling.c.obj) : error LNK2019: unresolved external symbol __iob_func referenced in function llvm_gcda_start_file

Unless Clang upstream resolves it I wouldn't expect this feature on Windows.

[LebedevRI]

Ah, ok then :)