[build-script] build LLVMTestingSupport only if target is generated

Otherwise the build will fail if we pass `--no-llvm-include-tests` or we
set directly `LLVM_INCLUDE_TESTS` directly to `FALSE`/`OFF`

Addresses rdar://153562845

Author: edymtt

utils/swift_build_support/swift_build_support/products/llvm.py

@@ -271,10 +271,7 @@ def build(self, host_target):
                     'llvm-size'
                 ])
         else:
-            # We build LLVMTestingSupport unconditionally
-            # to support scenarios where tests are run
-            # outside of `build-script` (e.g. with `run-test`)
-            build_targets = ['all', 'LLVMTestingSupport']
+            build_targets = ['all']
 
             if self.args.llvm_ninja_targets_for_cross_compile_hosts and \
                self.is_cross_compile_target(host_target):
@@ -422,6 +419,12 @@ def build(self, host_target):
             llvm_cmake_options.define('LLVM_INCLUDE_TESTS', 'NO')
             llvm_cmake_options.define('CLANG_INCLUDE_TESTS', 'NO')
 
+        if ("-DLLVM_INCLUDE_TESTS=NO" not in llvm_cmake_options
+            and "-DLLVM_INCLUDE_TESTS:BOOL=FALSE" not in llvm_cmake_options):
+            # This supports scenarios where tests are run
+            # outside of `build-script` (e.g. with `run-test`)
+            build_targets.append('LLVMTestingSupport')
+
         build_root = os.path.dirname(self.build_dir)
         host_machine_target = targets.StdlibDeploymentTarget.host_target().name
         host_build_dir = os.path.join(build_root, 'llvm-{}'.format(