Turn off is_official_build in the Rust Host Build Tools toolchain

Tools built to be used during the build process don't need PGO and
other official build things. This works around a bug on Mac for
chrome.exe where Rust gives the linker -plugin-opt flags it doesn't
understand: rust-lang/rust#60059

However the bug will be unresolved for other build targets that are
link-driven by Rust.

R=brucedawson@chromium.org

Bug: 1386212
Change-Id: I21824ad484048f0bc283454579f2f603acf3fa99
Cq-Include-Trybots: luci.chromium.try:win-rust-x64-rel,win-rust-x64-dbg,linux-rust-x64-rel,linux-rust-x64-dbg,android-rust-arm64-rel,android-rust-arm64-dbg,android-rust-arm32-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4545355
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Auto-Submit: danakj <danakj@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1146226}
NOKEYCHECK=True
GitOrigin-RevId: df7d81e33033a594ff56d5ab8387aa1f13cd1c39

toolchain/apple/toolchain.gni

@@ -807,8 +807,14 @@ template("apple_toolchain") {
   }
 
   if (enable_rust && current_toolchain == default_toolchain) {
-    # Make an additional toolchain which uses the prebuilt stdlib shipped with
-    # rustc.
+    # Make an additional toolchain which is used for making tools that are run
+    # on the host machine as part of the build process (such as proc macros
+    # and Cargo build scripts). This toolchain uses the prebuilt stdlib that
+    # comes with the compiler, so it doesn't have to wait for the stdlib to be
+    # built before building other stuff. And this ensures its proc macro
+    # outputs have the right ABI to be loaded by the compiler, and it can be
+    # used to compile build scripts that are part of the stdlib that is built
+    # for the default toolchain.
     single_apple_toolchain("${target_name}_for_rust_host_build_tools") {
       assert(defined(invoker.toolchain_args),
              "Toolchains must declare toolchain_args")
@@ -823,8 +829,12 @@ template("apple_toolchain") {
         # Populate toolchain args from the invoker.
         forward_variables_from(invoker.toolchain_args, "*")
         toolchain_for_rust_host_build_tools = true
+
+        # The host build tools are static release builds to make the Chromium
+        # build faster. They do not need PGO etc, so no official builds.
         is_debug = false
         is_component_build = false
+        is_official_build = false
       }
     }
   }

toolchain/gcc_toolchain.gni

@@ -827,8 +827,14 @@ template("gcc_toolchain") {
   }
 
   if (enable_rust && current_toolchain == default_toolchain) {
-    # Make an additional toolchain which uses the prebuilt stdlib shipped with
-    # rustc.
+    # Make an additional toolchain which is used for making tools that are run
+    # on the host machine as part of the build process (such as proc macros
+    # and Cargo build scripts). This toolchain uses the prebuilt stdlib that
+    # comes with the compiler, so it doesn't have to wait for the stdlib to be
+    # built before building other stuff. And this ensures its proc macro
+    # outputs have the right ABI to be loaded by the compiler, and it can be
+    # used to compile build scripts that are part of the stdlib that is built
+    # for the default toolchain.
     single_gcc_toolchain("${target_name}_for_rust_host_build_tools") {
       assert(defined(invoker.toolchain_args),
              "Toolchains must declare toolchain_args")
@@ -848,6 +854,7 @@ template("gcc_toolchain") {
         # build faster.
         is_debug = false
         is_component_build = false
+        is_official_build = false
       }
     }
   }

toolchain/win/toolchain.gni

@@ -582,8 +582,14 @@ template("msvc_toolchain") {
   }
 
   if (enable_rust && current_toolchain == default_toolchain) {
-    # Make an additional toolchain which uses the prebuilt stdlib shipped with
-    # rustc.
+    # Make an additional toolchain which is used for making tools that are run
+    # on the host machine as part of the build process (such as proc macros
+    # and Cargo build scripts). This toolchain uses the prebuilt stdlib that
+    # comes with the compiler, so it doesn't have to wait for the stdlib to be
+    # built before building other stuff. And this ensures its proc macro
+    # outputs have the right ABI to be loaded by the compiler, and it can be
+    # used to compile build scripts that are part of the stdlib that is built
+    # for the default toolchain.
     single_msvc_toolchain("${target_name}_for_rust_host_build_tools") {
       assert(defined(invoker.toolchain_args),
              "Toolchains must declare toolchain_args")
@@ -600,9 +606,10 @@ template("msvc_toolchain") {
         toolchain_for_rust_host_build_tools = true
 
         # The host build tools are static release builds to make the Chromium
-        # build faster.
+        # build faster. They do not need PGO etc, so no official builds.
         is_debug = false
         is_component_build = false
+        is_official_build = false
       }
     }
   }