[lld] Allow opt-out from building lld via --skip-build-lld

Author: kubamracek

utils/build_swift/build_swift/driver_arguments.py

@@ -830,8 +830,10 @@ def create_argument_parser():
     option('--build-ninja', toggle_true,
            help='build the Ninja tool')
 
-    option(['--build-lld'], toggle_true('build_lld'),
+    option(['--build-lld'], toggle_true('build_lld'), default=True,
            help='build lld as part of llvm')
+    option(['--skip-build-lld'], toggle_false('build_lld'),
+           help='skip building lld as part of llvm')
 
     option('--skip-build-clang-tools-extra',
            toggle_false('build_clang_tools_extra'),

utils/swift_build_support/swift_build_support/products/llvm.py

@@ -324,13 +324,14 @@ def build(self, host_target):
         if self.args.build_clang_tools_extra:
             llvm_enable_projects.append('clang-tools-extra')
 
-        # Always build lld -- on non-Darwin so we can always have a
+        # Building lld is on by default -- on non-Darwin so we can always have a
         # linker that is compatible with the swift we are using to
         # compile the stdlib, but on Darwin too for Embedded Swift use cases.
         #
         # This makes it easier to build target stdlibs on systems that
         # have old toolchains without more modern linker features.
-        llvm_enable_projects.append('lld')
+        if self.args.build_lld:
+            llvm_enable_projects.append('lld')
 
         llvm_cmake_options.define('LLVM_ENABLE_PROJECTS',
                                   ';'.join(llvm_enable_projects))