temporarily disable MinGW builds

.appveyor.yml

@@ -2,10 +2,13 @@ environment:
   matrix:
     - TARGET: x86_64-pc-windows-msvc
     - TARGET: i686-pc-windows-msvc
-    - TARGET: x86_64-pc-windows-gnu
-      MSYS_BITS: 64
-    - TARGET: i686-pc-windows-gnu
-      MSYS_BITS: 32
+    # Temporarily disable MinGW builds due to https://github.com/rust-lang/rust/issues/47048.
+    # Once that issue is fixed, presumably by https://github.com/rust-lang/rust/pull/51989,
+    # we should reenable them.
+    # - TARGET: x86_64-pc-windows-gnu
+    #   MSYS_BITS: 64
+    # - TARGET: i686-pc-windows-gnu
+    #   MSYS_BITS: 32
 
 install:
   - ps: Start-FileDownload "https://static.rust-lang.org/dist/rust-nightly-${env:TARGET}.exe"