[llvmlinux] Added the ability to choose from multiple clangs

[Sedat Dilek]

Hi Behan,

first of all, a big thank-you for the realization to use a stable
toolchain from LLVM-project.

For many (lazy!? like me) people and quick-testers this means to
reduce download-time and build-time as the toolchain has not to be
downloaded/built via the llvmlinux-buildsystem.

As you know, I made dozens of builds to finally get a working Linux
v3.10 llvmlinux-compiled kernel.
As you know, my focus is and was to build with a stable toolchain
(from LLVM-project).
It is due to my efforts that above mentioned toolchain was (1.) tested
well and thus is (2.) to be known good.

As you can see many projects promote x86_64 arch (LLVM-project offers
a prebuilt/prebuild toolchain).
So, the main focus of LLVMLinux-project should be IMHO the same.
Stabilize x86_64 first and other arches will follow... (...BTW, other
developers will be attracted, believe me :-).)

So, it's nice to see that my idea is now upstream.
But never forget to give credits. This is a sign of respect.
Due to the Linux-kernel development credit-system I would expect a
"Reported-by/Tested-by/Suggested-by".
I hope this happened by accident.

As a last remark: The spelling of "prebuilt" VS. "prebuild" <---
Please, use one of them.

"toolchain/clang/clang-prebuilt.mk" <--- "prebuil*t*"

versus

"prebuil*d*"

+${CLANG}: ${LLVMSTATE}/clang-prebuild
+clang-unpack: ${LLVMSTATE}/clang-prebuild
+${LLVMSTATE}/clang-prebuild: ${CLANG_TMPDIR}/${CLANG_TAR}
+       @rm -rf ${LLVMSTATE}/clang-prebuild ${CLANG_PATH}
${CLANG_TMPDIR}/${CLANG_TAR}

If you ask me, I vote for "prebuild" in all cases (even it is
grammatically wrong and not past-tense).

Regards,
- Sedat -

[1] http://git.linuxfoundation.org/?p=llvmlinux.git;a=commitdiff;h=3f1ee5b1d21e362b35c4240d07a5e888004c20ed