[CMake] Use separate namespace for demangling symbols used by runtime

This matches the behavior introduced with #30733.

Addresses rdar://142550635

Author: edymtt

Runtimes/Core/CMakeLists.txt

@@ -124,6 +124,11 @@ add_compile_definitions(
   $<$<BOOL:${SwiftCore_ENABLE_UNICODE_DATA}>:-DSWIFT_STDLIB_ENABLE_UNICODE_DATA> # Stubs
   $<$<BOOL:${SwiftCore_ENABLE_ENVIRONMENT}>:-DSWIFT_STDLIB_HAS_ENVIRON> # Concurrency, runtime, shims, platform overlay
   $<$<BOOL:${SwiftCore_ENABLE_BACKDEPLOYMENT_SUPPORT}>:-DSWIFT_STDLIB_SUPPORT_BACK_DEPLOYMENT> # Concurrency, Compatibility override, magic symbols
+  # Target libraries that include libDemangling must define the name to use for
+  # the inline namespace to distinguish symbols from those built for the
+  # compiler, in order to avoid possible ODR violations if both are statically
+  # linked into the same binary. (see also commit message for 5b1daa9055c99904c84862ecc313641fd9b26e63)
+  $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_INLINE_NAMESPACE=__runtime> # Demangling, runtime, Concurrency, RemoteInspection, SwiftRemoteMirror, swift-reflection-test
   $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_THREADING_${SwiftCore_THREADING_PACKAGE}>
   $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_RUNTIME_ENABLE_LEAK_CHECKER=$<BOOL:${SwiftCore_ENABLE_RUNTIME_LEAK_CHECKER}>>
   $<$<COMPILE_LANGUAGE:C,CXX>:-DSWIFT_RUNTIME_CLOBBER_FREED_OBJECTS=$<BOOL:${SwiftCore_ENABLE_CLOBBER_FREED_OBJECTS}>>)