ci: workspace mcpp bootstrap pin -> 0.0.108 (#282)

* ci: workspace mcpp bootstrap pin -> 0.0.107 (released + indexed)

0.0.107 is on both mirrors with matching sha256, xim-pkgindex#416 is merged, and
`xlings install mcpp@0.0.107` resolves and installs from a clean XLINGS_HOME.

* ci: bootstrap pin -> 0.0.108 (supersedes the 0.0.107 bump)

0.0.108 lands the second half of the explicit-ninja-goals fallout: 0.0.107 fixed
the missing soname alias, this one fixes the Windows command-line overflow. Pin
straight to it rather than land an intermediate bump.

Author: Sunrisepeak

.xlings.json

@@ -1,5 +1,5 @@
 {
   "workspace": {
-    "mcpp": "0.0.106"
+    "mcpp": "0.0.108"
   }
 }