Get swiftLLVMSupport building

This patch gets the LLVM Support object files building.

Author: etcwilde

Runtimes/Core/CMakeLists.txt

@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.26...3.29)
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake/modules")
+project(SwiftCore LANGUAGES C CXX Swift VERSION 6.1)
+
+# The Swift standard library is not intended for use as a sub-library as part of
+# another project. It is tightly coupled with the compiler version.
+if(NOT PROJECT_IS_TOP_LEVEL)
+  message(FATAL_ERROR "Swift Core must build as a standalone project")
+endif()
+include(CompilerSettings)
+
+include_directories(include)
+
+add_subdirectory(LLVMSupport)

Runtimes/Core/LLVMSupport/CMakeLists.txt

@@ -0,0 +1,7 @@
+add_library(swiftLLVMSupport OBJECT
+  ErrorHandling.cpp
+  Hashing.cpp
+  MemAlloc.cpp
+  SmallPtrSet.cpp
+  SmallVector.cpp
+  StringRef.cpp)

Runtimes/Core/cmake/modules/CompilerSettings.cmake

@@ -0,0 +1,17 @@
+# Use C+17
+set(SwiftCore_MIN_CXX_STANDARD 17)
+# Unset CMAKE_CXX_STANDARD if it's too low and in the CMakeCache.txt
+if($CACHE{CMAKE_CXX_STANDARD} AND $CACHE{CMAKE_CXX_STANDARD} LESS ${SwiftCore_MIN_CXX_STANDARD})
+  message(WARNING "Resetting cache value for CMAKE_CXX_STANDARD to ${SwiftCore_MIN_CXX_STANDARD}")
+  unset(CMAKE_CXX_STANDARD CACHE)
+endif()
+
+# Allow manually specified CMAKE_CXX_STANDARD if it's greater than the minimum
+# required C++ version
+if(DEFINED CMAKE_CXX_STANDARD AND CMAKE_CXX_STANDARD LESS ${SwiftCore_MIN_CXX_STANDARD})
+  message(FATAL_ERROR "Requested CMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} which is less than the minimum C++ standard ${SwiftCore_MIN_CXX_STANDARD}")
+endif()
+
+set(CMAKE_CXX_STANDARD ${SwiftCore_MIN_CXX_STANDARD} CACHE STRING "C++ standard to conform to")
+set(CMAKE_CXX_STANDARD_REQUIRED YES)
+set(CMAKE_CXX_EXTENSIONS NO)