Fix seamonkey-2.53.7.1 for rustc-1.52.0.

introduction/welcome/changelog.xml

@@ -45,6 +45,9 @@
    <listitem>
      <para>May 9th, 2021</para>
      <itemizedlist>
+       <listitem>
+         <para>[ken] - Fix seamonkey build breakage with rust-1.52.0.</para>
+       </listitem>
        <listitem>
          <para>[ken] - Update to rustc-1.52.0 (security fix). Fixes
          <ulink url="&blfs-ticket-root;15000">#15000</ulink>.</para>

xsoft/graphweb/seamonkey.xml

@@ -291,7 +291,8 @@ EOF</userinput></screen>
       commands:
     </para>
 
-<screen><userinput>CC=gcc CXX=g++ make -f client.mk</userinput></screen>
+<screen><userinput>RUSTC_BOOTSTRAP=encoding_rs,packed_simd \
+CC=gcc CXX=g++ make -f client.mk</userinput></screen>
 
     <note>
       <para>
@@ -320,6 +321,15 @@ cp -v $(find -name seamonkey.1 | head -n1) /usr/share/man/man1</userinput></scre
   <sect2 role="commands">
     <title>Command Explanations</title>
 
+    <para>
+      <command>RUSTC_BOOTSTRAP=encoding_rs,packed_simd</command>: With
+      <application>rustc-1.52.0</application> crates can no longer set
+      `RUSTC_BOOTSTRAP` themselves because it subverts the stability guarantee
+      of Rust. The crates encoding_rs v0.8.16 and packed_simd v0.3.4 are both
+      affected, setting the environment variable like this allows the package
+      to compile.
+    </para>
+
     <para>
       <command>make -f client.mk</command>: Mozilla products are packaged to
       allow the use of a configuration file which can be used to pass the