Better errors for invalid --cc parameters.

When you specified something odd for --cc you'd get a really cryptic "Permission Denied" error when we go to check the compiler version. Do better checking on the --cc executable first, and error if it is not  1) executable and 2) a file.  Also, make the compile test function in the same way.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@194516 91177308-0d34-0410-b5e6-96231b3b80d8
Bootstrapify summary report edit UI.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@194517 91177308-0d34-0410-b5e6-96231b3b80d8
Add a json interface to the Summary Report view.

git-svn-id: https://llvm.org/svn/llvm-project/lnt/trunk@194518 91177308-0d34-0410-b5e6-96231b3b80d8