CMake: Set SWIFT_STDLIB_HAS_DLADDR/DLSYM

Parts of the runtime depend on DLADDR/DLSYM. Use CMake to determine if
these functions are available and then define the
`SWIFT_STDLIB_HAS_DLADDR`/`SWIFT_STDLIB_HAS_DLSYM` when the function is
available.

`SWIFT_STDLIB_HAS_DLADDR` is used in several source files in the runtime
library. `SWIFT_STDLIB_HAS_DLSYM` only appears to be used in
`ThreadSanitizer.cpp`.

Author: etcwilde

Runtimes/Core/CMakeLists.txt

@@ -62,6 +62,7 @@ set(SwiftCore_VENDOR_MODULE_DIR "${SwiftCore_CMAKE_MODULES_DIR}/vendor"
   CACHE FILEPATH "Location for private build system extension")
 
 include(GNUInstallDirs)
+include(CheckSymbolExists)
 include(AvailabilityMacros)
 include(CompilerSettings)
 include(DefaultSettings)
@@ -70,6 +71,9 @@ include(PlatformInfo)
 include(gyb)
 include(Plist)
 
+check_symbol_exists("dladdr" "dlfcn.h" SwiftCore_HAS_DLADDR)
+check_symbol_exists("dlsym" "dlfcn.h" SwiftCore_HAS_DLSYM)
+
 include("${SwiftCore_VENDOR_MODULE_DIR}/Settings.cmake" OPTIONAL)
 
 defaulted_option(SwiftCore_ENABLE_LIBRARY_EVOLUTION "Generate ABI resilient runtime libraries")

Runtimes/Core/runtime/CMakeLists.txt

@@ -84,7 +84,9 @@ target_compile_definitions(swiftRuntime
     $<$<BOOL:${SwiftCore_ENABLE_MALLOC_TYPE}>:-DSWIFT_STDLIB_HAS_MALLOC_TYPE>
     $<$<BOOL:${SwiftCore_BACKTRACER_PATH}>:-DSWIFT_RUNTIME_FIXED_BACKTRACER_PATH="${SwiftCore_BACKTRACER_PATH}">
     $<$<BOOL:${SwiftCore_ENABLE_STDLIB_TRACING}>:-DSWIFT_STDLIB_TRACING>
-    $<$<BOOL:${SwiftCore_ENABLE_SHORT_MANGLING_LOOKUPS}>:-DSWIFT_STDLIB_SHORT_MANGLING_LOOKUPS>)
+    $<$<BOOL:${SwiftCore_ENABLE_SHORT_MANGLING_LOOKUPS}>:-DSWIFT_STDLIB_SHORT_MANGLING_LOOKUPS>
+    $<$<BOOL:${SwiftCore_HAS_DLADDR}>:-DSWIFT_STDLIB_HAS_DLADDR>
+    $<$<BOOL:${SwiftCore_HAS_DLSYM}>:-DSWIFT_STDLIB_HAS_DLSYM>)
 
 target_include_directories(swiftRuntime PRIVATE
   "${PROJECT_BINARY_DIR}/include"