CMake: SwiftCore: Add back SWIFT_STDLIB_SUPPORTS_BACKTRACE_REPORTING

So, despite the name, this is not the same as enabling backtracing....
Somehow. Anyway, this was a macro from the old build that we want in the
new build.

rdar://142440689

Author: etcwilde

Runtimes/Core/CMakeLists.txt

@@ -72,6 +72,7 @@ include(gyb)
 include(Plist)
 
 check_symbol_exists("asl_log" "asl.h" SwiftCore_HAS_ASL)
+check_symbol_exists("backtrace" "execinfo.h" SwiftCore_HAS_BACKTRACE)
 check_symbol_exists("dladdr" "dlfcn.h" SwiftCore_HAS_DLADDR)
 check_symbol_exists("dlsym" "dlfcn.h" SwiftCore_HAS_DLSYM)
 
@@ -100,6 +101,7 @@ defaulted_option(SwiftCore_ENABLE_STDLIB_TRACING "Enable tracing in the runtime.
 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)
+option(SwiftCore_ENABLE_BACKTRACE_REPORTING "Build with backtrace reporting support" ${SwiftCore_HAS_BACKTRACE})
 
 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

@@ -99,7 +99,8 @@ target_compile_definitions(swiftRuntime
     $<$<BOOL:${SwiftCore_HAS_DLSYM}>:-DSWIFT_STDLIB_HAS_DLSYM>
     $<$<BOOL:${SwiftCore_ENABLE_FILESYSTEM_SUPPORT}>:-DSWIFT_STDLIB_HAS_FILESYSTEM>
     $<$<AND:$<BOOL:${SwiftCore_ENABLE_FILESYSTEM_SUPPORT}>,$<COMPILE_LANGUAGE:C,CXX>>:-DSWIFT_ARCH="${SwiftCore_ARCH_SUBDIR}">
-    $<$<AND:$<BOOL:${SwiftCore_ENABLE_FILESYSTEM_SUPPORT}>,$<COMPILE_LANGUAGE:C,CXX>>:-DSWIFT_LIB_SUBDIR="${SwiftCore_PLATFORM_SUBDIR}">)
+    $<$<AND:$<BOOL:${SwiftCore_ENABLE_FILESYSTEM_SUPPORT}>,$<COMPILE_LANGUAGE:C,CXX>>:-DSWIFT_LIB_SUBDIR="${SwiftCore_PLATFORM_SUBDIR}">
+    $<$<BOOL:${SwiftCore_ENABLE_BACKTRACE_REPORTING}>:-DSWIFT_STDLIB_SUPPORTS_BACKTRACE_REPORTING>)
 
 target_include_directories(swiftRuntime PRIVATE
   "${PROJECT_BINARY_DIR}/include"