[Libomptarget] Pass '-Werror=global-constructors' to the libomptarget build (#88531)

Summary:
A runtime library should not have global constructors. Everything is now
expected to go through the init methods. This patch ensures that global
constructors will not accidentally be introduced.

Author: jhuber6

offload/CMakeLists.txt

@@ -136,6 +136,8 @@ include(LibomptargetGetDependencies)
 # Set up testing infrastructure.
 include(OpenMPTesting)
 
+check_cxx_compiler_flag(-Werror=global-constructors OFFLOAD_HAVE_WERROR_CTOR)
+
 # LLVM source tree is required at build time for libomptarget
 if (NOT LIBOMPTARGET_LLVM_INCLUDE_DIRS)
   message(FATAL_ERROR "Missing definition for LIBOMPTARGET_LLVM_INCLUDE_DIRS")
@@ -207,6 +209,9 @@ set(offload_compile_flags -fno-exceptions)
 if(NOT LLVM_ENABLE_RTTI)
   set(offload_compile_flags ${offload_compile_flags} -fno-rtti)
 endif()
+if(OFFLOAD_HAVE_WERROR_CTOR)
+  list(APPEND offload_compile_flags -Werror=global-constructors)
+endif()
 
 # TODO: Consider enabling LTO by default if supported.
 # https://cmake.org/cmake/help/latest/module/CheckIPOSupported.html can be used

offload/src/CMakeLists.txt

@@ -69,8 +69,8 @@ foreach(plugin IN LISTS LIBOMPTARGET_PLUGINS_TO_BUILD)
   target_link_libraries(omptarget PRIVATE omptarget.rtl.${plugin})
 endforeach()
 
-target_compile_options(omptarget PUBLIC ${offload_compile_flags})
-target_link_options(omptarget PUBLIC ${offload_link_flags})
+target_compile_options(omptarget PRIVATE ${offload_compile_flags})
+target_link_options(omptarget PRIVATE ${offload_link_flags})
 
 # libomptarget.so needs to be aware of where the plugins live as they
 # are now separated in the build directory.