Add GCCBootstrapMacOS

It turns out that to build `GCC` for macOS in the streamlined fashion
that I wish to do in the `GCC` recipe here, we need a bootstrapped GCC
targeting macOS first (you can't use `clang`).  So.... we build one
here, re-using as much from our `GCC` recipe as possible.

Author: staticfloat

bootstrap/GCCBootstrapMacOS/build_tarballs.jl

@@ -0,0 +1,34 @@
+using BinaryBuilder2
+
+include("../GCC/gcc_common.jl")
+
+for version in (v"14.2.0",)
+    build_tarballs(;
+        src_name = "GCCBootstrapMacOS",
+        src_version = version,
+        sources = [
+            gcc_version_sources[version]...,
+            DirectorySource("./patches-v$(version)"; follow_symlinks=true, target="patches"),
+        ],
+        script = string(
+            """
+            # By setting `GCC_ENABLE_BOOTSTRAP=true`, we opt-in to
+            # a bootstrapped GCC build and disable trying to use the target CToolchain
+            GCC_ENABLE_BOOTSTRAP=true
+            """,
+            script,
+        ),
+        platforms = [
+            CrossPlatform(Platform(arch(HostPlatform()), "linux") => Platform("aarch64", "macos")),
+            CrossPlatform(Platform(arch(HostPlatform()), "linux") => Platform("x86_64", "macos")),
+        ],
+        products = [
+            FileProduct("bin", :bindir),
+            ExecutableProduct("\${target}-gcc", :gcc),
+            ExecutableProduct("\${target}-g++", :gxx),
+        ],
+        build_spec_generator = gcc_build_spec_generator,
+        meta,
+        duplicate_extraction_handling = :ignore_all,
+    )
+end

bootstrap/GCCBootstrapMacOS/patches-v14.2.0

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+../GCC/patches-v14.2.0

bootstrap/GCCBootstrapMacOS/patches-v9.4.0

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+../GCC/patches-v9.4.0