android: add support for LLVM 3.7.0 for marshmallow

android: add support for LLVM 3.7.0 for marshmallow

The changes add support for LLVM 3.7.0 for marshmallow,
while keeping support for LLVM 3.5.0 with lollipop.

MESA_LLVM_VERSION_PATCH=0 is compatible with radeonsi build in lollipop-x86,
since mesa 11.0 and newer do not check anymore for LLVM 3.5.2

This changes, combined with specific R600 patches for external/llvm,
enable building gallium radeonsi driver in marshmallow-x86.

The patch is applicable to 11.2.0devel, 11.1 and 11.0 branches.