use lto=thin to reduce memory pressure when building gkrust
https://bugzilla.mozilla.org/show_bug.cgi?id=1644409
https://bugzilla.mozilla.org/show_bug.cgi?id=1640982

Index: config/makefiles/rust.mk
--- config/makefiles/rust.mk.orig
+++ config/makefiles/rust.mk
@@ -92,7 +92,8 @@ ifndef rustflags_sancov
 # Never enable when coverage is enabled to work around https://github.com/rust-lang/rust/issues/90045.
 ifndef MOZ_CODE_COVERAGE
 ifeq (,$(findstring gkrust_gtest,$(RUST_LIBRARY_FILE)))
-cargo_rustc_flags += -Clto$(if $(filter full,$(MOZ_LTO_RUST_CROSS)),=fat)
+cargo_rustc_flags += -Clto=thin
+export CARGO_PROFILE_RELEASE_LTO=thin
 endif
 # We need -Cembed-bitcode=yes for all crates when using -Clto.
 RUSTFLAGS += -Cembed-bitcode=yes