[build][rust] Disable mutable-noalias in rust builds

It was recently discovered that mutable-noalias can lead to
miscompilations (see rust-lang/rust#84958).
This CL disables that optimization for all rust builds.

Bug: 76184
Tests: Manually reviewed basic functionality on devices, relying on CI
for broader coverage

Change-Id: I6555e38c74270cba0d4741b7826ac1705b123010
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/526741
Commit-Queue: Paul Faria <paulfaria@google.com>
Reviewed-by: Adam Perry <adamperry@google.com>
Reviewed-by: Tyler Mandry <tmandry@google.com>

build/config/BUILDCONFIG.gn

@@ -282,7 +282,11 @@ is_efi_toolchain =
 shlib_toolchain = "${toolchain_variant.base}${toolchain_variant.suffix}-shared"
 
 # Prepend the prefix configs, if any, before the default ones.
-default_common_binary_configs = toolchain_variant.prefix_configs
+default_common_binary_configs =
+    toolchain_variant.prefix_configs + [
+      # TODO(fxbug.dev/76297) Remove this to re-enable mutable-noalias.
+      "//build/config/rust:no_mutable_noalias",
+    ]
 
 # Note that Zircon toolchains and non-Zircon ones have a very different set
 # of default configs for all target types.

build/config/rust/BUILD.gn

@@ -86,6 +86,11 @@ config("v0_symbol_mangling") {
   }
 }
 
+# TODO(fxbug.dev/76297) Remove this to re-enable mutable-noalias.
+config("no_mutable_noalias") {
+  rustflags = [ "-Zmutable-noalias=off" ]
+}
+
 config("allow_unknown_lints") {
   rustflags = [ "-Aunknown-lints" ]
 }