[runtimes] Fix incorrect comment about the purpose of LLVM_DEFAULT_TARGET_TRIPLE

5beec6f added LLVM_DEFAULT_TARGET_TRIPLE to the runtimes build with
a comment, however I believe that comment had been copied from the LLVM
build tree. In the context of the runtimes, LLVM_DEFAULT_TARGET_TRIPLE
is used to set what targets we are building for, not the target for which
we "generate code".

Differential Revision: https://reviews.llvm.org/D114007

Author: ldionne

runtimes/CMakeLists.txt

@@ -117,7 +117,7 @@ find_package(Python3 REQUIRED COMPONENTS Interpreter)
 include(GetHostTriple)
 get_host_triple(LLVM_HOST_TRIPLE)
 set(LLVM_DEFAULT_TARGET_TRIPLE "${LLVM_HOST_TRIPLE}" CACHE STRING
-  "Default target for which LLVM will generate code.")
+  "Default target for which the runtimes will be built.")
 
 option(LLVM_INCLUDE_TESTS "Generate build targets for the runtimes unit tests." ON)
 option(LLVM_INCLUDE_DOCS "Generate build targets for the runtimes documentation." ON)