Adding support for overriding LLVM_ENABLE_RUNTIMES for runtimes builds.
Adding support for overriding LLVM_ENABLE_RUNTIMES for runtimes builds.

Second attempt: Now with ';' -> '|' replacement.

On some platforms, certain runtimes are not supported. For runtimes builds of
those platforms it would be nice if we could disable certain runtimes (ie
libunwind on Windows).

Differential Revision: https://reviews.llvm.org/D67195



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@372784 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm