Disable testing CoreCLR

Author: Omar Tawfik

build.cmd

@@ -124,7 +124,7 @@ if /i '%ARG%' == 'microbuild' (
 
     set TEST_COMPILERUNIT=1
     set TEST_NET40_COREUNIT=1
-    set TEST_CORECLR=1
+    set TEST_CORECLR=0
     set TEST_PORTABLE_COREUNIT=1
     set TEST_VS=1
     set TEST_FSHARP_SUITE=1