Remove the sysroot restriction from building GCDAProfiling.c.

We really need the C standard library to be available to implement the
profiling runtime library reasonably, and replicating everything in the
SDKs tree really isn't addressing any problems we have. Notably, all of
the sanitizer runtimes take the same approach, and this isn't a library
which could end up in a bootstrapping problem where the system headers
aren't even available.

This will hopefully prevent subsequent changes which start using various
other bits of C standard library to make things more debuggable.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@184798 91177308-0d34-0410-b5e6-96231b3b80d8
Address a few of the issues in GCDAProfiling I noted when looking
through Bill's patch:

1) Correctly test the file descriptor after the sceond attempt at
   creating the file.
2) Make the filename a global so that we can issue error messages from
   other routines.
3) Check errno in several places and print it out so that errors are
   easier to track down.

I don't really expect any of these to fix the current failures I'm
seeing, but I'm hopeful they'll at least let me debug them.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@184799 91177308-0d34-0410-b5e6-96231b3b80d8
Remove the sysroot (or isysroot) restriction from the GCDAProfile.c
runtime in the Makefile build system as well. Sorry for the temporary
fallout, it took me a while to find these bits.

Bill, I'm not at all confident of the change for Darwin and iOS, but as
discussed we're completely blocked on fixing this. Anyways, please
review and let me know if this will work for you guys. If necessary,
I can work with you to rig up an errno.h stub for Darwin, but I expect
that to be... moderately challenging.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@184805 91177308-0d34-0410-b5e6-96231b3b80d8