[Backtracing] Really only build for OS X.

Added some extra code to AddSwiftStdlib.cmake so executable targets can
specify target SDKs the same way libraries currently can.

Updated the Backtracing targets to specify just OS X for now.

Author: al45tair

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -2680,6 +2680,7 @@ function(add_swift_target_executable name)
     SWIFT_MODULE_DEPENDS_FROM_SDK
     SWIFT_MODULE_DEPENDS_MACCATALYST
     SWIFT_MODULE_DEPENDS_MACCATALYST_UNZIPPERED
+    TARGET_SDKS
   )
 
   # Parse the arguments we were given.
@@ -2706,7 +2707,16 @@ function(add_swift_target_executable name)
   # All Swift executables depend on the swiftSwiftOnoneSupport library.
   list(APPEND SWIFTEXE_TARGET_SWIFT_MODULE_DEPENDS SwiftOnoneSupport)
 
-  foreach(sdk ${SWIFT_SDKS})
+  # If target SDKs are not specified, build for all known SDKs.
+  if("${SWIFTEXE_TARGET_TARGET_SDKS}" STREQUAL "")
+    set(SWIFTEXE_TARGET_TARGET_SDKS ${SWIFT_SDKS})
+  endif()
+  list_replace(SWIFTEXE_TARGET_TARGET_SDKS ALL_APPLE_PLATFORMS "${SWIFT_DARWIN_PLATFORMS}")
+
+  list_intersect(
+    "${SWIFTEXE_TARGET_TARGET_SDKS}" "${SWIFT_SDKS}" SWIFTEXE_TARGET_TARGET_SDKS)
+
+  foreach(sdk ${SWIFTEXE_TARGET_TARGET_SDKS})
     set(THIN_INPUT_TARGETS)
 
     # Collect architecture agnostic SDK module dependencies

stdlib/public/Backtracing/CMakeLists.txt

@@ -55,4 +55,6 @@ add_swift_target_library(swift_Backtracing ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} I
 
   INSTALL_IN_COMPONENT stdlib
   MACCATALYST_BUILD_FLAVOR "zippered"
+
+  TARGET_SDKS OSX
 )

stdlib/public/CMakeLists.txt

@@ -156,10 +156,7 @@ if(SWIFT_BUILD_STDLIB)
     add_subdirectory(Observation)
   endif()
 
-  # Make this macOS only for now.
-  if(OSX IN_LIST SWIFT_SDKS)
-    add_subdirectory(Backtracing)
-  endif()
+  add_subdirectory(Backtracing)
 endif()
 
 if(SWIFT_BUILD_STDLIB OR SWIFT_BUILD_REMOTE_MIRROR)

stdlib/public/libexec/swift-backtrace/CMakeLists.txt

@@ -9,4 +9,6 @@ add_swift_target_executable(swift-backtrace BUILD_WITH_STDLIB
     _Backtracing
 
   INSTALL_IN_COMPONENT stdlib
-  COMPILE_FLAGS -parse-as-library)
+  COMPILE_FLAGS -parse-as-library
+
+  TARGET_SDKS OSX)

test/Backtracing/BacktraceWithLimit.swift

@@ -4,7 +4,7 @@
 // RUN: %target-run %t/BacktraceWithLimit | %FileCheck %s
 
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=ios
+// REQUIRES: OS=macosx
 
 import _Backtracing
 

test/Backtracing/BacktraceWithLimitAndTop.swift

@@ -4,7 +4,7 @@
 // RUN: %target-run %t/BacktraceWithLimitAndTop | %FileCheck %s
 
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=ios
+// REQUIRES: OS=macosx
 
 import _Backtracing
 

test/Backtracing/SimpleAsyncBacktrace.swift

@@ -5,7 +5,7 @@
 
 // REQUIRES: concurrency
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=iOS || OS=watchOS || OS=tvOS
+// REQUIRES: OS=macosx
 // REQUIRES: concurrency_runtime
 // UNSUPPORTED: back_deployment_runtime
 

test/Backtracing/SimpleBacktrace.swift

@@ -4,7 +4,7 @@
 // RUN: %target-run %t/SimpleBacktrace | %FileCheck %s
 
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=iOS || OS=watchOS || OS=tvOS
+// REQUIRES: OS=macosx
 
 func level1() {
   level2()

test/Backtracing/SymbolicatedBacktrace.swift

@@ -4,7 +4,7 @@
 // RUN: %target-run %t/SymbolicatedBacktrace | %FileCheck %s
 
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=ios || OS=watchOS || OS=tvOS
+// REQUIRES: OS=macosx
 
 import _Backtracing
 

test/Backtracing/SymbolicatedBacktraceInline.swift

@@ -4,7 +4,7 @@
 // RUN: %target-run %t/SymbolicatedBacktraceInline | %FileCheck %s
 
 // REQUIRES: executable_test
-// REQUIRES: OS=macosx || OS=ios || OS=watchOS || OS=tvOS
+// REQUIRES: OS=macosx
 
 import _Backtracing