[build-script] Split the build-script-impl pipeline into two pipelines so I can put a build-script product pipeline in between.

This is where I am going to put the stage 2 swift. The reason why I need to do
this is that I need libdispatch, foundation, etc on Linux to use the stage2
compiler.

Author: gottesmm

utils/swift_build_support/swift_build_support/build_script_invocation.py

@@ -526,7 +526,7 @@ def compute_product_pipelines(self):
         # the build-script code base. The main difference is that these are all
         # build, tested, and installed all at once instead of performing build,
         # test, install like a normal build-script product.
-        builder.begin_impl_pipeline(should_run_epilogue_operations=True)
+        builder.begin_impl_pipeline(should_run_epilogue_operations=False)
 
         # If --skip-build-llvm is passed in, LLVM cannot be completely disabled, as
         # Swift still needs a few LLVM targets like tblgen to be built for it to be
@@ -541,6 +541,11 @@ def compute_product_pipelines(self):
                                  is_enabled=self.args.build_swift)
         builder.add_impl_product(products.LLDB,
                                  is_enabled=self.args.build_lldb)
+
+        # Begin a new build-script-impl pipeline that builds libraries that we
+        # build as part of build-script-impl but that we should eventually move
+        # onto build-script products.
+        builder.begin_impl_pipeline(should_run_epilogue_operations=True)
         builder.add_impl_product(products.LibDispatch,
                                  is_enabled=self.args.build_libdispatch)
         builder.add_impl_product(products.Foundation,
@@ -617,13 +622,17 @@ def execute(self):
 
         # Execute each "product pipeline".
         for index in range(len(product_pipelines)):
+            perform_epilogue_opts = last_impl_index == index
             pipeline = product_pipelines[index]
+
             # Skip empty pipelines.
             if len(pipeline) == 0:
+                if perform_epilogue_opts:
+                    self._execute_merged_host_lipo_core_action()
                 continue
+
             is_impl = pipeline[0].is_build_script_impl_product()
             if is_impl:
-                perform_epilogue_opts = last_impl_index == index
                 self._execute_impl(pipeline, all_hosts, perform_epilogue_opts)
             else:
                 assert(index != last_impl_index)

validation-test/BuildSystem/core_lipo_and_non_core_epilogue_opts.test

@@ -0,0 +1,16 @@
+# REQUIRES: standalone_build
+# REQUIRES: OS=macosx
+
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --dry-run --cmake %cmake --infer --swiftpm --verbose-build 2>&1 | %FileCheck %s
+
+# Make sure we build swift, llvm, llbuild, then do core lipo, then build
+# swiftpm, and finally finish by running the rest of the epilogue operations.
+
+# CHECK: cmake -G Ninja {{.*}}llvm-project/llvm
+# CHECK: cmake -G Ninja {{.*}}swift
+# CHECK: --only-execute {{.*}}-llbuild-build
+# CHECK: --only-execute merged-hosts-lipo-core
+# CHECK: --- Building swiftpm ---
+# CHECK: --only-execute merged-hosts-lipo

validation-test/BuildSystem/default_build_still_performs_epilogue_opts_after_split.test

@@ -0,0 +1,11 @@
+# RUN: %empty-directory(%t)
+# RUN: mkdir -p %t
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --verbose-build --dry-run --cmake %cmake 2>&1 | %FileCheck %s
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --verbose-build --dry-run --cmake %cmake --infer 2>&1 | %FileCheck %s
+# RUN: SKIP_XCODE_VERSION_CHECK=1 SWIFT_BUILD_ROOT=%t %swift_src_root/utils/build-script --verbose-build --dry-run --cmake %cmake --infer --swiftpm 2>&1 | %FileCheck %s
+
+# Make sure we run the merged hosts lipo step regardless of whether or not we
+# are building anything from the 2nd build-script-impl phase with or without
+# infer.
+
+# CHECK: --only-execute merged-hosts-lipo

validation-test/BuildSystem/infer_dumps_deps_if_verbose_build.test

@@ -10,17 +10,20 @@
 # CHECK: Initial Product List:
 # CHECK:     earlyswiftdriver
 # CHECK: -- Build Graph Inference --
-# CHECK: Initial Product List:
+# CHECK-NEXT: Initial Product List:
 # CHECK:     llvm
 # CHECK:     swift
+# CHECK-NOT: llbuild
 # CHECK: -- Build Graph Inference --
-# CHECK: Initial Product List:
+# CHECK-NEXT: Initial Product List:
 # CHECK:     swiftpm
+# CHECK-NOT: llbuild
 # CHECK: Final Build Order:
 # CHECK:     earlyswiftdriver
 # CHECK:     cmark
 # CHECK:     llvm
 # CHECK:     swift
+# CHECK:     llbuild
 # CHECK:     swiftpm
 
 # Ensure early SwiftDriver is built first