[llvm] [runtimes][cmake] Keep default PIC behavior consistent in standalone build (PR #205797)

[Louis Dionne via llvm-commits]

================
@@ -205,6 +205,12 @@ endif()
 # Avoid checking whether the compiler is working.
 set(LLVM_COMPILER_CHECKED ON)
 
+# Match default PIC behavior between bootstrap and standalone runtime builds.
+# Required before including HandleLLVMOptions.
+if (NOT CMAKE_SYSTEM_NAME MATCHES "OS390")
----------------
ldionne wrote:

Why this `if`? IMO this should be achieved using a custom CMake cache on that platform if they don't want the same PIC mode we normally use.

https://github.com/llvm/llvm-project/pull/205797