appveyor.yml: try mingw-w64 gcc again, pass -x

appveyor.yml

@@ -7,18 +7,17 @@ version: "{branch}.{build}"
 environment:
   global:
     GOPATH: c:\gopath
+    CC: c:\mingw-w64\i686-5.3.0-posix-dwarf-rt_v4-rev0\mingw32\bin\gcc.exe
 
 install:
   - go version
-  - cd c:\gopath\src\github.com\ethereum\go-ethereum
-  - set MSYSTEM=MINGW64
-  - C:\msys64\usr\bin\bash -l -c "gcc --version"
+  - "%CC% --version"
 
 build_script:
-  - C:\msys64\usr\bin\bash -l -c "go run build/ci.go install"
+  - go run build\ci.go install
 
 test_script:
-  - C:\msys64\usr\bin\bash -l -c "go run build/ci.go test -vet -coverage"
+  - go run build\ci.go test -vet -coverage
 
 after_build:
   - go run build\ci.go archive -type zip

build/ci.go

@@ -148,7 +148,7 @@ func doInstall(cmdline []string) {
 	}
 
 	goinstall := goTool("install", makeBuildFlags(*commitHash)...)
-	goinstall.Args = append(goinstall.Args, "-v")
+	goinstall.Args = append(goinstall.Args, "-v", "-x")
 	goinstall.Args = append(goinstall.Args, packages...)
 	build.MustRun(goinstall)
 }