Bug 1273625 - rust: Update win32 builders to 1.8.0 stable. r=mshal

We were using 1.9 beta for i586 support. Now that it's no longer
necessary we can revert to the stable release.

This is a repack of the 1.8.0 upstream stable build targetting
only i686-pc-windows-msvc.

MozReview-Commit-ID: 7ieQ9steK5k

browser/config/tooltool-manifests/win32/releng.manifest

@@ -6,9 +6,9 @@
 "filename": "mozmake.exe"
 },
 {
-"version": "1.9.0-beta.1 (37a2869af 2016-04-12)",
-"size": 96983375,
-"digest": "180118e83948c24c3df2e78f02468d9011c8583c1df36d25481f74c302e9085f442133884adf431b8c05567ce1d5dfb05915cdc0bd6303d599452cad350c8de4",
+"version": "rustc 1.8.0 (db2939409 2016-04-11)",
+"size": 78733276,
+"digest": "96ab09cd667ed854efeeca41881a92c9fdc5f3cdeff9b02b12c514183c0b54a21dee8574367abe532429e04660681a1f6c37f6d22cc877d63fbcca7b986d3495",
 "algorithm": "sha512",
 "filename": "rustc.tar.bz2",
 "unpack": true