build: Mirror LLVM+Xcode-specific build-script-impl logic in CMake build-script product

This fixes the behavior of `--xcode`, which was relying on this logic and was
compromised when LLVM became a build-script product.

Author: AnthonyLatsis

utils/swift_build_support/swift_build_support/products/cmake_product.py

@@ -71,7 +71,13 @@ def build_with_cmake(self, build_targets, build_type, build_args,
                            env=env)
 
         if not self.args.skip_build or self.product_name() == "llvm":
+            cmake_opts = [self.build_dir, "--config", build_type]
+
             if self.args.cmake_generator == "Xcode":
+                # CMake automatically adds "--target ALL_BUILD" if we don't
+                # pass this.
+                cmake_opts += ["--target", "ZERO_CHECK"]
+
                 # Xcode generator uses "ALL_BUILD" instead of "all".
                 # Also, xcodebuild uses -target instead of bare names.
                 build_targets = build_targets[:]
@@ -82,12 +88,11 @@ def build_with_cmake(self, build_targets, build_type, build_args,
 
                 # Xcode can't restart itself if it turns out we need to reconfigure.
                 # Do an advance build to handle that.
-                shell.call(["env"] + cmake_build
-                           + [self.build_dir, "--config", build_type])
+                shell.call(["env"] + cmake_build + cmake_opts)
 
-            shell.call(["env"] + cmake_build
-                       + [self.build_dir, "--config", build_type, "--"]
-                       + build_args + build_targets)
+            shell.call(
+                ["env"] + cmake_build + cmake_opts + ["--"] + build_args + build_targets
+            )
 
     def test_with_cmake(self, executable_target, results_targets,
                         build_type, build_args, test_env=None):

validation-test/BuildSystem/skip_build_xcode.test

@@ -0,0 +1,14 @@
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --xcode --release --swift-darwin-supported-archs="$(uname -m)" --dry-run --cmake %cmake 2>&1 | %FileCheck %s
+
+# REQUIRES: standalone_build
+# REQUIRES: OS=macosx
+
+# Make sure we pass '--target ZERO_CHECK' (otherwise CMake automatically adds
+# '--target ALL_BUILD' and we end up building everything) and build the bare
+# minimum required to configure Swift.
+#
+# CHECK: --- Building llvm ---
+# CHECK: env {{.+}}/cmake --build {{.+}}/Xcode-ReleaseAssert/llvm-macosx-{{.+}} --config Release --target ZERO_CHECK{{$}}
+# CHECK-NEXT: env {{.+}}/cmake --build {{.+}}/Xcode-ReleaseAssert/llvm-macosx-{{.+}} --config Release --target ZERO_CHECK -- -target llvm-tblgen -target clang-resource-headers -target intrinsics_gen -target clang-tablegen-targets -target FileCheck -target not -target llvm-nm -target llvm-size{{$}}