fix invalid assumption about the executable module in Target::Install()

Target::Install() was assuming the module at index 0 was the executable.
This is often true, but not guaranteed to be the case.  The
TestInferiorChanged.py test highlighted this when run against iOS.
After the binary is replaced in the middle of the test, it becomes the
last module in the list.  The rest of the Target::Install() logic then
clobbers the executable file by using whatever happens to be the first
module in the target module list.

This change also marks the TestInferiorChanged.py test as a no-debug-info
test.

llvm-svn: 273960