When cross-debugging from Windows host, names of source files typically 
print without a directory prefix.  So I was getting a spurious failure like:

Breakpoint 2, bar (y=1) at solib-vanish-lib2.c:21
21        return y + 1;                 /* break here */
(gdb) FAIL: gdb.base/solib-vanish.exp: continue to breakpoint: bar

because the regexp expected a "/" in the filename.  This is easy to fix, 
and in fact in the past I've committed a number of similar patches to 
adjust other testcases expecting a directory prefix as well.  So I've 
committed this one as obvious.

-Sandra