CMake: Verify os_signpost_*/os_log with tracing

Adding check to CMake to verify that we have the os_signpost and os_log
API available in order to accept enabling the runtime tracing.

Author: etcwilde

Runtimes/Core/CMakeLists.txt

@@ -110,7 +110,7 @@ defaulted_option(SwiftCore_ENABLE_CONCURRENCY "Enable Concurrency runtime suppor
 defaulted_option(SwiftCore_ENABLE_REMOTE_MIRROR "Enable RemoteMirror runtime support")
 defaulted_option(SwiftCore_ENABLE_DIRECT_RETAIN_RELEASE "Use direct retain release in the runtime/stdlib")
 defaulted_set(SwiftCore_CONCURRENCY_GLOBAL_EXECUTOR STRING "Default Concurrency global executor implementation")
-option(SwiftCore_ENABLE_STDLIB_TRACING "Enable tracing in the runtime. Assumes the precense of os_log(3) and the os_signpost(3) API." OFF)
+option(SwiftCore_ENABLE_STDLIB_TRACING "Enable tracing in the runtime. Requires os_log(3) and the os_signpost(3) API." OFF)
 option(SwiftCore_ENABLE_COMMANDLINE_SUPPORT "Enable command line argument support" ON)
 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)

Runtimes/Core/runtime/CMakeLists.txt

@@ -72,6 +72,14 @@ if(SwiftCore_ENABLE_FILESYSTEM_SUPPORT AND (NOT SwiftCore_ARCH_SUBDIR OR NOT Swi
   message(SEND_ERROR "Filesystem support requires setting `SwiftCore_ARCH_SUBDIR` and `SwiftCore_PLATFORM_SUBDIR`")
 endif()
 
+if(SwiftCore_ENABLE_STDLIB_TRACING)
+  check_symbol_exists("os_signpost_interval_begin" "os/signpost.h" SwiftCore_HAS_OS_SIGNPOST)
+  check_symbol_exists("os_log" "os/log.h" SwiftCore_HAS_OS_LOG)
+  if(NOT SwiftCore_HAS_OS_LOG OR NOT SwiftCore_HAS_OS_SIGNPOST)
+    message(SEND_ERROR "Tracing requires 'os_signpost' and 'os_log' APIs")
+  endif()
+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