[runtimes] Fix incorrect comment about the purpose of LLVM_DEFAULT_TARGET_TRIPLE

[ldionne]

Summary

5beec6fb04e7 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".

[phosek]

LGTM

[DavidSpickett]

I believe that comment had been copied from the LLVM build tree

Correct, thanks for updating it.

runtimes/CMakeLists.txt

 include(HandleLLVMOptions)
 
 find_package(Python3 REQUIRED COMPONENTS Interpreter)
 
 # Host triple is used by tests to check if they are running natively.
 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)
 option(LLVM_ENABLE_SPHINX "Use Sphinx to generate the runtimes documentation." OFF)
 
 # Use libtool instead of ar if you are both on an Apple host, and targeting Apple.
 if(CMAKE_HOST_APPLE AND APPLE)
   include(UseLibtool)