gdb/testsuite: tighten patterns in build-id-no-debug-warning.exp

gdb/testsuite: tighten patterns in build-id-no-debug-warning.exp

Tighten the expected output pattern in the test script:

  gdb.debuginfod/build-id-no-debug-warning.exp

While working on some other patch I broke GDB such that this warning:

  warning: "FILENAME": separate debug info file has no debug info

(which is generated in build-id.c) didn't actually include the
FILENAME any more -- yet this test script continued to pass.  It turns
out that this script doesn't actually check for FILENAME.

This commit extends the test pattern to check for the full warning
string, including FILENAME, and also removes some uses of '.*' to make
the test stricter.