[PATCH] Update testsuite mechanism to allow object files as source files.

[Tom Tromey]

Joseph> On general free software and reproducible builds principles:
Joseph> * The source for any checked-in object file should be checked in.
Joseph> * That source should include comments giving all information required to 
Joseph> be able to reproduce the object file byte-for-byte

In the past we tried this kind of thing, by taking the assembly
generated by the compiler, then editing it and checking it in.

However, IMO, this turned out to be a pain.  The hand editing was often
not sufficiently documented, and the tests were still
architecture-dependent.  Once or twice I think someone has had to edit
the .S file later, which is error-prone.  Also, the earliest test suite
additions like this didn't include the original source, making this
harder to handle.

The "DWARF assembler" in the test suite avoids all this, at least for
tests that require particular debuginfo.  The main drawbacks of this
approach are (again IMO) that sometimes it's a pain to write the DWARF
by hand, and that sometimes the assembler framework itself needs
upgrades before one can even begin.  However, the tests are much more
robust.

I'd encourage the extension of the latter approach as much as possible.
It isn't perfect but IME has been better on the whole.

Tom