GDB JIT support: move .text segment check earlier

If the file is to be purely interpreted, the .text segment will be of
zero length and won't get a segment mapped. Currently this will cause a
check failure, but we should just exit if the GDB JIT support cannot be
enabled.

Change-Id: Iea3834ee5c1313837ebcbe3b58ecd2dc924c1b1e
1 file changed