Bug 1258796 - Re-enable rust on win32 builds. r=mshal

We're still using a i686-pc-windows-msvc rust stdlib,
but now that bug 1255869 we have runtime protection against
calling the sse2 code it contains.

Reverts bug 1253456.

--HG--
extra : rebase_source : 28c7399eb9f90f2865c41eb394a5949e05a632ff

browser/config/mozconfigs/win32/beta

@@ -13,4 +13,6 @@ mk_add_options MOZ_PGO=1
 ac_add_options --enable-official-branding
 ac_add_options --enable-verify-mar
 
+. "$topsrcdir/build/mozconfig.rust"
+
 . "$topsrcdir/build/mozconfig.common.override"

browser/config/mozconfigs/win32/nightly

@@ -6,5 +6,7 @@ ac_add_options --enable-verify-mar
 
 ac_add_options --with-branding=browser/branding/nightly
 
+. "$topsrcdir/build/mozconfig.rust"
+
 . "$topsrcdir/build/mozconfig.common.override"
 . "$topsrcdir/build/mozconfig.cache"

browser/config/mozconfigs/win32/release

@@ -19,4 +19,6 @@ ac_add_options --enable-verify-mar
 # defines.sh during the beta cycle
 export BUILDING_RELEASE=1
 
+. "$topsrcdir/build/mozconfig.rust"
+
 . "$topsrcdir/build/mozconfig.common.override"