[NFC][asan] Guard implemetation with ASAN_INTERCEPT_SWAPCONTEXT

Author: vitalybuka

compiler-rt/lib/asan/asan_linux.cpp

@@ -208,7 +208,7 @@ void AsanCheckIncompatibleRT() {
 }
 #endif // SANITIZER_ANDROID
 
-#if !SANITIZER_ANDROID
+#  if ASAN_INTERCEPT_SWAPCONTEXT
 void ReadContextStack(void *context, uptr *stack, uptr *ssize) {
   ucontext_t *ucp = (ucontext_t*)context;
   *stack = (uptr)ucp->uc_stack.ss_sp;
@@ -220,13 +220,7 @@ void ResetContextStack(void *context) {
   ucp->uc_stack.ss_sp = nullptr;
   ucp->uc_stack.ss_size = 0;
 }
-#  else
-void ReadContextStack(void *context, uptr *stack, uptr *ssize) {
-  UNIMPLEMENTED();
-}
-
-void ResetContextStack(void *context) { UNIMPLEMENTED(); }
-#  endif
+#  endif  // ASAN_INTERCEPT_SWAPCONTEXT
 
 void *AsanDlSymNext(const char *sym) {
   return dlsym(RTLD_NEXT, sym);

compiler-rt/lib/asan/asan_mac.cpp

@@ -95,12 +95,6 @@ void FlushUnneededASanShadowMemory(uptr p, uptr size) {
   ReleaseMemoryPagesToOS(MemToShadow(p), MemToShadow(p + size));
 }
 
-void ReadContextStack(void *context, uptr *stack, uptr *ssize) {
-  UNIMPLEMENTED();
-}
-
-void ResetContextStack(void *context) { UNIMPLEMENTED(); }
-
 // Support for the following functions from libdispatch on Mac OS:
 //   dispatch_async_f()
 //   dispatch_async()

compiler-rt/lib/asan/asan_win.cpp

@@ -263,12 +263,6 @@ void AsanCheckDynamicRTPrereqs() {}
 
 void AsanCheckIncompatibleRT() {}
 
-void ReadContextStack(void *context, uptr *stack, uptr *ssize) {
-  UNIMPLEMENTED();
-}
-
-void ResetContextStack(void *context) { UNIMPLEMENTED(); }
-
 void AsanOnDeadlySignal(int, void *siginfo, void *context) { UNIMPLEMENTED(); }
 
 bool PlatformUnpoisonStacks() { return false; }