[llvm] [llvm][CMake] Introduce LLVM_RUNTIME_<project>_BUILD in CMake (PR #88934)

[Michael Klemm via llvm-commits]

================
@@ -208,6 +208,36 @@ foreach(entry ${runtimes})
   list(APPEND RUNTIME_NAMES ${name})
 endforeach()
 
+# Set LLVM_RUNTIME_<project>_BUILD variables if a sub-project is enabled to be built as
+# a runtime.  As with LLVM_TOOL_<project>_BUILD, the LLVM_RUNTIME_<project>_BUILD variables
+# should be not directly used from the CMake configuration command line.
+foreach(proj ${LLVM_SUPPORTED_RUNTIMES})
----------------
mjklemm wrote:

Good question.  I'm not qualified to answer it, though.

https://github.com/llvm/llvm-project/pull/88934