[SwiftCompilerSources] Enable use of the -min-runtime-version option.

Turn on the use of `-min-runtime-version` when building the compiler.

rdar://121522431

Author: al45tair

CMakeLists.txt

@@ -101,9 +101,11 @@ include(FetchContent)
 check_language(Swift)
 if(CMAKE_Swift_COMPILER)
   enable_language(Swift)
+  set(DEFAULT_SWIFT_MIN_RUNTIME_VERSION "${CMAKE_Swift_COMPILER_VERSION}")
 else()
   message(STATUS "WARNING! Did not find a host compiler swift?! Can not build
                   any compiler host sources written in Swift")
+  set(DEFAULT_SWIFT_MIN_RUNTIME_VERSION)
 endif()
 
 # A convenience pattern to match Darwin platforms. Example:
@@ -464,6 +466,10 @@ set(SWIFT_DARWIN_MODULE_ARCHS "" CACHE STRING
 targets on Darwin platforms. These targets are in addition to the full \
 library targets.")
 
+set(SWIFT_MIN_RUNTIME_VERSION "${DEFAULT_SWIFT_MIN_RUNTIME_VERSION}" CACHE STRING
+  "Specify the minimum version of the runtime that we target when building \
+the compiler itself. This is used on non-Darwin platforms to ensure \
+that it's possible to build the compiler using host tools.")
 
 #
 # User-configurable Android specific options.

SwiftCompilerSources/CMakeLists.txt

@@ -106,7 +106,13 @@ function(add_swift_compiler_modules_library name)
       "-Xcc" "-std=c++17"
       "-Xcc" "-DCOMPILED_WITH_SWIFT" "-Xcc" "-DSWIFT_TARGET"
       "-Xcc" "-UIBOutlet" "-Xcc" "-UIBAction" "-Xcc" "-UIBInspectable")
+
   if (NOT BOOTSTRAPPING_MODE STREQUAL "HOSTTOOLS")
+    if(SWIFT_MIN_RUNTIME_VERSION)
+      list(APPEND swift_compile_options
+        "-Xfrontend" "-min-runtime-version"
+        "-Xfrontend" "${SWIFT_MIN_RUNTIME_VERSION}")
+    endif()
     list(APPEND swift_compile_options "-Xfrontend" "-disable-implicit-string-processing-module-import")
   endif()
 

utils/build-script-impl

@@ -116,6 +116,9 @@ KNOWN_SETTINGS=(
     darwin-toolchain-require-use-os-runtime       "0"               "When setting up a plist for a toolchain, require the users of the toolchain to link against the OS instead of the packaged toolchain runtime. 0 for false, 1 for true"
     darwin-xcrun-toolchain                        "default"         "the name of the toolchain to use on Darwin"
 
+    ## Runtime options
+    min-runtime-version                ""                "Used to specify the minimum host runtime version when building the compiler on non-Darwin platforms"
+
     ## WebAssembly/WASI Options
     wasi-sysroot                                  ""                "An absolute path to the wasi-sysroot that will be used as a libc implementation for Wasm builds"
 
@@ -750,6 +753,12 @@ function set_build_options_for_host() {
                 )
             fi
 
+            if [[ ! -z "${MIN_RUNTIME_VERSION}" ]]; then
+                swift_cmake_options+=(
+                    -DSWIFT_MIN_RUNTIME_VERSION="${MIN_RUNTIME_VERSION}"
+                )
+            fi
+
             swift_cmake_options+=(
                 -DSWIFT_DARWIN_DEPLOYMENT_VERSION_OSX="${DARWIN_DEPLOYMENT_VERSION_OSX}"
                 -DSWIFT_DARWIN_DEPLOYMENT_VERSION_IOS="${DARWIN_DEPLOYMENT_VERSION_IOS}"