[CMake] Setting the LLVM_TARGET_TRIPLE macro based on the LLVM_DEFAULT_TARGET_TRIPLE

After D137870, LLVM_TARGET_TRIPLE is no longer defined on the runtime
path into compiler-rt. This patch creates a common block of code to set
LLVM_TARGET_TRIPLE equal to the default for both the llvm- and runtime-
paths.

Differential Revision: https://reviews.llvm.org/D138864

Author: nicolerabjohn

llvm/CMakeLists.txt

@@ -857,17 +857,8 @@ else()
   endif()
 endif()
 
-set(LLVM_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE_default}" CACHE STRING
-  "Default target for which LLVM will generate code." )
-if (TARGET_TRIPLE)
-  message(WARNING "TARGET_TRIPLE is deprecated and will be removed in a future release. "
-                  "Please use LLVM_DEFAULT_TARGET_TRIPLE instead.")
-  set(LLVM_TARGET_TRIPLE "${TARGET_TRIPLE}")
-else()
-  set(LLVM_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
-endif()
-message(STATUS "LLVM host triple: ${LLVM_HOST_TRIPLE}")
-message(STATUS "LLVM default target triple: ${LLVM_DEFAULT_TARGET_TRIPLE}")
+include(SetTargetTriple)
+set_llvm_target_triple()
 
 if(WIN32 OR CYGWIN)
   if(BUILD_SHARED_LIBS OR LLVM_BUILD_LLVM_DYLIB)

llvm/cmake/modules/SetTargetTriple.cmake

@@ -0,0 +1,13 @@
+macro(set_llvm_target_triple)
+  set(LLVM_DEFAULT_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE_default}" CACHE STRING
+  "Default target for which LLVM will generate code." )
+  if (TARGET_TRIPLE)
+    message(WARNING "TARGET_TRIPLE is deprecated and will be removed in a future release. "
+    "Please use LLVM_DEFAULT_TARGET_TRIPLE instead.")
+    set(LLVM_TARGET_TRIPLE "${TARGET_TRIPLE}")
+  else()
+    set(LLVM_TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
+  endif()
+  message(STATUS "LLVM host triple: ${LLVM_HOST_TRIPLE}")
+  message(STATUS "LLVM default target triple: ${LLVM_DEFAULT_TARGET_TRIPLE}")
+endmacro()

runtimes/CMakeLists.txt

@@ -176,6 +176,9 @@ endif()
 # This can be used to detect whether we're in the runtimes build.
 set(LLVM_RUNTIMES_BUILD ON)
 
+include(SetTargetTriple)
+set_llvm_target_triple()
+
 foreach(entry ${runtimes})
   get_filename_component(projName ${entry} NAME)