appveyor: add mingw qt5.7 debug wang-bin#709. fix msbuild error

Author: wang-bin

appveyor.yml

@@ -22,6 +22,13 @@ environment:
     mode: release
     QTDIR: C:\Qt\5.7\msvc2015
 
+  - arch: 32
+    cc: MinGW
+    qt: 5.7
+    toolchain_version: 530
+    mode: debug
+    QTDIR: C:\Qt\5.7\mingw53_32
+
   - arch: 32
     cc: MinGW
     qt: 5.4

tools/ci/win/build.bat

@@ -6,7 +6,7 @@ if "%cc%" == "MinGW" (
 ) else (
   if "%mode%" == "debug" (
     qmake %APPVEYOR_BUILD_FOLDER% -r -tp vc "CONFIG+=debug"
-    msbuild /m /p:Configuration=DEBUG
+    msbuild /p:Configuration=DEBUG
   ) else (
     qmake %APPVEYOR_BUILD_FOLDER%
     where jom