libctf, ld: diagnose corrupted CTF header cth_strlen

The last section in a CTF dict is the string table, at an offset
represented by the cth_stroff header field.  Its length is recorded in
the next field, cth_strlen, and the two added together are taken as the
size of the CTF dict.  Upon opening a dict, we check that none of the
header offsets exceed this size, and we check when uncompressing a
compressed dict that the result of the uncompression is the same length:
but CTF dicts need not be compressed, and short ones are not.
Uncompressed dicts just use the ctf_size without checking it.  This
field is thankfully almost unused: it is mostly used when reserializing
a dict, which can't be done to dicts read off disk since they're
read-only.

However, when opening an uncompressed foreign-endian dict we have to
copy it out of the mmaped region it is stored in so we can endian-
swap it, and we use ctf_size when doing that.  When the cth_strlen is
corrupt, this can overrun.

Fix this by checking the ctf_size in all uncompressed cases, just as we
already do in the compressed case.  Add a new test.

This came to light because various corrupted-CTF raw-asm tests had an
incorrect cth_strlen: fix all of them so they produce the expected
error again.

libctf/
	PR libctf/28933
	* ctf-open.c (ctf_bufopen_internal): Always check uncompressed
	CTF dict sizes against the section size in case the cth_strlen is
	corrupt.

ld/
	PR libctf/28933
	* testsuite/ld-ctf/diag-strlen-invalid.*: New test,
	derived from diag-cttname-invalid.s.
	* testsuite/ld-ctf/diag-cttname-invalid.s: Fix incorrect cth_strlen.
	* testsuite/ld-ctf/diag-cttname-null.s: Likewise.
	* testsuite/ld-ctf/diag-cuname.s: Likewise.
	* testsuite/ld-ctf/diag-parlabel.s: Likewise.
	* testsuite/ld-ctf/diag-parname.s: Likewise.