Link sanitizers with libgcc on Linux, allow undefined symbols

Author: edymtt

utils/swift_build_support/swift_build_support/products/llvm.py

@@ -291,7 +291,13 @@ def build(self, host_target):
         llvm_cmake_options.define('LLVM_INCLUDE_DOCS:BOOL', 'TRUE')
         llvm_cmake_options.define('LLVM_ENABLE_LTO:STRING', self.args.lto_type)
         llvm_cmake_options.define('COMPILER_RT_INTERCEPT_LIBDISPATCH', 'ON')
-        llvm_cmake_options.define('RUNTIMES_CMAKE_ARGS', '-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR:BOOL=OFF')
+        llvm_cmake_options.define(
+            'RUNTIMES_CMAKE_ARGS',
+            '-DLLVM_ENABLE_PER_TARGET_RUNTIME_DIR:BOOL=OFF;'
+            # This preserves the behaviour we had when using LLVM_BUILD_EXTERNAL COMPILER_RT --
+            # that is, not requiring the linker to complaining if symbols used by TSan are
+            # undefined (namely the ones for Blocks Runtime)
+            '-DSANITIZER_COMMON_LINK_FLAGS:STRING=-Wl,-z,undefs')
 
         if self.args.build_embedded_stdlib and system() == "Darwin":
             # Ask for Mach-O cross-compilation builtins (for Embedded Swift)
@@ -306,8 +312,6 @@ def build(self, host_target):
                 not self.is_cross_compile_target(host_target):
             llvm_enable_runtimes.append('compiler-rt')
             build_targets.append("runtimes")
-            # This is needed to build correctly TSan under Linux
-            llvm_cmake_options.define('COMPILER_RT_USE_BUILTINS_LIBRARY', 'ON')
 
         if self.args.build_clang_tools_extra:
             llvm_enable_projects.append('clang-tools-extra')