Removed llvm-cov.test from Other folder.

More comprehensive llvm-cov tests were added to tools/llvm-cov.
With the new update to the ABI, we should not look for installations
of MinGW older than 4.7 with incompatible C++ libraries.

This patch makes clang look for all MinGW versions from 4.7:

  4.7.0, 4.7.1, 4.7.2, 4.7.3
  4.8.0, 4.8.1, 4.8.2.