http://www.wg9s.com/comm-253/patches/seamonkey-253-patches/mozilla-release/patches/1670538-87a1.patch
https://bugs.gentoo.org/789981

--- seamonkey-2.53.7.1/config/rules.mk
+++ seamonkey-2.53.7.1/config/rules.mk
@@ -861,16 +861,27 @@
 # Versions of rust >= 1.45 need -Cembed-bitcode=yes for all crates when
 # using -Clto.
 ifeq (,$(filter 1.37.% 1.38.% 1.39.% 1.40.% 1.41.% 1.42.% 1.43.% 1.44.%,$(RUSTC_VERSION)))
 RUSTFLAGS += -Cembed-bitcode=yes
 endif
 endif
 endif
 
+ifndef RUSTC_BOOTSTRAP
+ifeq (,$(filter 1.47.% 1.48.% 1.49.%,$(RUSTC_VERSION)))
+# RUSTC_BOOTSTRAP := gkrust_shared,qcms for later
+RUSTC_BOOTSTRAP := gkrust_shared
+ifdef MOZ_RUST_SIMD
+RUSTC_BOOTSTRAP := $(RUSTC_BOOTSTRAP),encoding_rs,packed_simd
+endif
+export RUSTC_BOOTSTRAP
+endif
+endif
+
 rustflags_override = RUSTFLAGS='$(MOZ_RUST_DEFAULT_FLAGS) $(RUSTFLAGS)'
 
 ifdef MOZ_MSVCBITS
 # If we are building a MozillaBuild shell, we want to clear out the
 # vcvars.bat environment variables for cargo builds. This is because
 # a 32-bit MozillaBuild shell on a 64-bit machine will try to use
 # the 32-bit compiler/linker for everything, while cargo/rustc wants
 # to use the 64-bit linker for build.rs scripts. This conflict results
--- seamonkey-2.53.7.1/toolkit/library/rust/shared/build.rs.1670538.later
+++ seamonkey-2.53.7.1/toolkit/library/rust/shared/build.rs.1670538.later
@@ -0,0 +1,16 @@
+--- build.rs
++++ build.rs
+@@ -17,12 +17,12 @@ fn main() {
+     } else if std::env::var("MOZ_AUTOMATION").is_ok() {
+         panic!("Builds on automation must use a version of rust for which we know how to hook OOM: want < {}, have {}",
+                max_oom_hook_version, ver);
+     }
+ 
+     // This is a rather awful thing to do, but we're only doing it on
+     // versions of rustc that are not going to change the unstable APIs
+     // we use from under us, all being already released or beta.
+-    if bootstrap {
++    if bootstrap && ver < Version::parse("1.50.0").unwrap() {
+         println!("cargo:rustc-env=RUSTC_BOOTSTRAP=1");
+     }
+ }