LLVM/Clang 3.7.0 support

[rayslava]

Currently git LLVM and Clang have version 3.7.0svn which causes

    configure: error: bad LLVM version: 3.7.0svn, need >=3.0svn

during configure.

[sanxiyn]

This is intentional, see #21998. You can use ./configure --disable-llvm-version-check if you want to try anyway.

[dotdash]

We're using a pretty up to date version of 3.7 now, so I'll close this.