[LLVM] Removes CMake work-arounds.

CMake older than 3.20.0 is no longer supported.
This removes work-arounds for no longer supported versions.

Reviewed By: kwk

Differential Revision: https://reviews.llvm.org/D152103

Author: mordante

llvm/CMakeLists.txt

@@ -1064,29 +1064,6 @@ if (UNIX AND ${CMAKE_SYSTEM_NAME} MATCHES "AIX")
           add_compile_definitions(_XOPEN_SOURCE=700)
           add_compile_definitions(_LARGE_FILE_API)
 
-  # CMake versions less than 3.16 set default linker flags to include -brtl, as
-  # well as setting -G when building libraries, so clear them out. Note we only
-  # try to clear the form that CMake will set as part of its initial
-  # configuration, it is still possible the user may force it as part of a
-  # compound option.
-  if(CMAKE_VERSION VERSION_LESS 3.16)
-    string(REGEX REPLACE "(^|[ \t]+)-Wl,-brtl([ \t]+|$)" " " CMAKE_EXE_LINKER_FLAGS  "${CMAKE_EXE_LINKER_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)-Wl,-brtl([ \t]+|$)" " " CMAKE_SHARED_LINKER_FLAGS  "${CMAKE_SHARED_LINKER_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)-Wl,-brtl([ \t]+|$)" " " CMAKE_MODULE_LINKER_FLAGS "${CMAKE_MODULE_LINKER_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)(-Wl,)?-G([ \t]+|$)" " " CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS
-      "${CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)(-Wl,)?-G([ \t]+|$)" " " CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS
-      "${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)(-Wl,)?-G([ \t]+|$)" " " CMAKE_SHARED_LIBRARY_CREATE_ASM_FLAGS
-      "${CMAKE_SHARED_LIBRARY_CREATE_ASM_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)-Wl,-G," " -Wl," CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS
-      "${CMAKE_SHARED_LIBRARY_CREATE_C_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)-Wl,-G," " -Wl," CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS
-      "${CMAKE_SHARED_LIBRARY_CREATE_CXX_FLAGS}")
-    string(REGEX REPLACE "(^|[ \t]+)-Wl,-G," " -Wl," CMAKE_SHARED_LIBRARY_CREATE_ASM_FLAGS
-      "${CMAKE_SHARED_LIBRARY_CREATE_ASM_FLAGS}")
-  endif()
-
   # Modules should be built with -shared -Wl,-G, so we can use runtime linking
   # with plugins.
   string(APPEND CMAKE_MODULE_LINKER_FLAGS " -shared -Wl,-G")

llvm/docs/CMakePrimer.rst

@@ -54,7 +54,7 @@ program. The example uses only CMake language-defined functions.
 
 .. code-block:: cmake
 
-   cmake_minimum_required(VERSION 3.15)
+   cmake_minimum_required(VERSION 3.20.0)
    project(HelloWorld)
    add_executable(HelloWorld HelloWorld.cpp)
 
@@ -64,7 +64,7 @@ block to define "APPLE" when targeting Apple platforms:
 
 .. code-block:: cmake
 
-   cmake_minimum_required(VERSION 3.15)
+   cmake_minimum_required(VERSION 3.20.0)
    project(HelloWorld)
    add_executable(HelloWorld HelloWorld.cpp)
    if(APPLE)