[Libomptarget] Reintroduce host architecture checks for device RTL

[jhuber6]

Summary

A previous patch removed the need to set the auxiliary architecture as
it was no longer needed for the clang invocation after moving to using
the clang frontend. However, this had a second use of preventing
unsupported host architectures from building the device runtime. This
caused failures when trying to build on 32-bit hosts for example.

Fixes #56699

[tianshilei1992]

openmp/libomptarget/DeviceRTL/CMakeLists.txt

22

I remember there is a bug report about the name of host arch is not consistent among different OSs. If we just want to disable build for 32-bit system, we might want something else.

[jhuber6]

Updating to use sizeof pointer instead to elimate support for 32-bit hosts.

[tianshilei1992]

LGTM

openmp/libomptarget/DeviceRTL/CMakeLists.txt

 set(LIBOMPTARGET_BUILD_DEVICERTL_BCLIB TRUE CACHE BOOL
   "Can be set to false to disable building this library.")
 
 if (NOT LIBOMPTARGET_BUILD_DEVICERTL_BCLIB)
   libomptarget_say("Not building DeviceRTL: Disabled by LIBOMPTARGET_BUILD_DEVICERTL_BCLIB")
   return()
 endif()
 
+# Check to ensure the host system is a supported host architecture.
+if(NOT ${CMAKE_SIZEOF_VOID_P} EQUAL "8")
+  libomptarget_say("Not building DeviceRTL: Runtime does not support 32-bit hosts")
+  return()
+endif()
+
 if (LLVM_DIR)
   # Builds that use pre-installed LLVM have LLVM_DIR set.
   # A standalone or LLVM_ENABLE_RUNTIMES=openmp build takes this route
   find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
   find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR}
     NO_DEFAULT_PATH)
   find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
   if ((NOT CLANG_TOOL) OR (NOT LINK_TOOL) OR (NOT OPT_TOOL))