LLVMFlang: Fix Fortran shared library creation on Apple platforms

LLVMFlang requires Apple-specific linker options to be forwarded through
`-Xlinker`.

Fixes: #27558

Modules/Platform/Apple-LLVMFlang-Fortran.cmake

@@ -0,0 +1,9 @@
+# Distributed under the OSI-approved BSD 3-Clause License.  See accompanying
+# file LICENSE.rst or https://cmake.org/licensing for details.
+
+# LLVM Flang requires Darwin linker flags to be passed through its linker
+# wrapper rather than directly to the compiler driver.
+set(CMAKE_Fortran_OSX_COMPATIBILITY_VERSION_FLAG "-Xlinker -compatibility_version -Xlinker ")
+set(CMAKE_Fortran_OSX_CURRENT_VERSION_FLAG "-Xlinker -current_version -Xlinker ")
+set(CMAKE_SHARED_MODULE_CREATE_Fortran_FLAGS "-Xlinker -bundle")
+set(CMAKE_SHARED_LIBRARY_SONAME_Fortran_FLAG "-Xlinker -install_name -Xlinker ")

Tests/Fortran/CMakeLists.txt

@@ -48,6 +48,9 @@ endif()
 
 add_library(hello STATIC hello.f)
 add_library(world ${_SHARED} world.f ${world_def})
+if(APPLE AND CMAKE_Fortran_COMPILER_ID STREQUAL "LLVMFlang")
+  set_target_properties(world PROPERTIES VERSION 1.2.3 SOVERSION 1)
+endif()
 add_executable(testf testf.f)
 target_link_libraries(testf hello world)