Use LLVM_USE_RUNTIMES to build compiler-rt by default

Addresses rdar://113972453

Author: edymtt

utils/build_swift/build_swift/driver_arguments.py

@@ -1398,7 +1398,7 @@ def create_argument_parser():
                 'separated options "-DCMAKE_VAR1=YES,-DCMAKE_VAR2=/tmp". Can '
                 'be called multiple times to add multiple such options.')
 
-    option('--llvm-build-compiler-rt-with-use-runtimes', toggle_true,
+    option('--llvm-build-compiler-rt-with-use-runtimes', toggle_false,
            help='Switch to LLVM_USE_RUNTIMES as the mechanism to build compiler-rt'
                 'It will become the default with LLVM 21, this flag is '
                 'meant to stage its introduction and account for edge cases')

utils/build_swift/tests/expected_options.py

@@ -232,7 +232,7 @@
     'lldb_build_variant': 'Debug',
     'lldb_build_with_xcode': '0',
     'llvm_assertions': True,
-    'llvm_build_compiler_rt_with_use_runtimes': False,
+    'llvm_build_compiler_rt_with_use_runtimes': True,
     'llvm_build_variant': 'Debug',
     'llvm_cmake_options': [],
     'llvm_enable_modules': False,
@@ -854,7 +854,7 @@ class BuildScriptImplOption(_BaseOption):
     AppendOption('--llvm-ninja-targets'),
     AppendOption('--llvm-ninja-targets-for-cross-compile-hosts'),
     AppendOption('--llvm-cmake-options'),
-    SetTrueOption('--llvm-build-compiler-rt-with-use-runtimes'),
+    SetFalseOption('--llvm-build-compiler-rt-with-use-runtimes'),
     AppendOption('--darwin-symroot-path-filters'),
 
     UnsupportedOption('--build-jobs'),