SwiftCore: CMake: Hook up filesystem flag

This hooks up the SWIFT_STDLIB_HAS_FILESYSTEM, which then requires
setting SWIFT_ARCH and SWIFT_LIB_SUBDIR macros for the backtracer.

Note: `FILESYSTEM` in this case does not refer to the C++ filesystem
header, but whether the platform you're building for has a filesystem.

Author: etcwilde

Runtimes/Core/CMakeLists.txt

@@ -95,6 +95,7 @@ defaulted_option(SwiftCore_ENABLE_BACKDEPLOYMENT_SUPPORT "Add symbols for runtim
 defaulted_option(SwiftCore_ENABLE_STDLIB_TRACING "Enable tracing in the runtime. Assumes the presence of os_log(3) and the os_signpost(3) API.")
 option(SwiftCore_ENABLE_UNICODE_DATA "Include unicode data in Swift runtimes" ON)
 option(SwiftCore_ENABLE_SHORT_MANGLING_LOOKUPS "Build with fast-path context descriptor lookups based on well-known short manglings." ON)
+option(SwiftCore_ENABLE_FILESYSTEM_SUPPORT "Build for systems that have a filesystem" ON)
 
 defaulted_option(SwiftCore_ENABLE_BACKTRACING "Enable backtracing runtime support")
 defaulted_set(SwiftCore_BACKTRACER_PATH STRING "Set a fixed path to the Swift backtracer")

Runtimes/Core/runtime/CMakeLists.txt

@@ -72,6 +72,15 @@ if(SwiftCore_ENABLE_RUNTIME_LEAK_CHECKER)
     Leaks.mm)
 endif()
 
+# runtime/Paths.cpp uses `SWIFT_ARCH` and `SWIFT_LIB_SUBDIR` to find the
+# subdirectory under `libexec` in which to find the backtracer.
+# Fail the configuration if it isn't set appropriately.
+# TODO: In the future, we might consider moving the backtracer up to
+# `libexec/swift` and drop the platform/architecture specific subdirectories
+if(SwiftCore_ENABLE_FILESYSTEM_SUPPORT AND (NOT SwiftCore_ARCH_SUBDIR OR NOT SwiftCore_PLATFORM_SUBDIR))
+  message(SEND_ERROR "Filesystem support requires setting `SwiftCore_ARCH_SUBDIR` and `SwiftCore_PLATFORM_SUBDIR`")
+endif()
+
 # TODO: Probably worth considering putting half of these in a RuntimeConfig.h.in
 #       file rather than pushing them through macro flags.
 target_compile_definitions(swiftRuntime
@@ -86,7 +95,8 @@ target_compile_definitions(swiftRuntime
     $<$<BOOL:${SwiftCore_ENABLE_STDLIB_TRACING}>:-DSWIFT_STDLIB_TRACING>
     $<$<BOOL:${SwiftCore_ENABLE_SHORT_MANGLING_LOOKUPS}>:-DSWIFT_STDLIB_SHORT_MANGLING_LOOKUPS>
     $<$<BOOL:${SwiftCore_HAS_DLADDR}>:-DSWIFT_STDLIB_HAS_DLADDR>
-    $<$<BOOL:${SwiftCore_HAS_DLSYM}>:-DSWIFT_STDLIB_HAS_DLSYM>)
+    $<$<BOOL:${SwiftCore_HAS_DLSYM}>:-DSWIFT_STDLIB_HAS_DLSYM>
+    $<$<BOOL:${SwiftCore_ENABLE_FILESYSTEM_SUPPORT}>:-DSWIFT_STDLIB_HAS_FILESYSTEM$<SEMICOLON>-DSWIFT_ARCH="${SwiftCore_ARCH_SUBDIR}"$<SEMICOLON>-DSWIFT_LIB_SUBDIR="${SwiftCore_PLATFORM_SUBDIR}">)
 
 target_include_directories(swiftRuntime PRIVATE
   "${PROJECT_BINARY_DIR}/include"