[gdb/testsuite] Modernize gdb.base/huge.exp

Rewrite test-case gdb.base/huge.exp:
- use build_executable rather than gdb_compile,
- use save_vars,
- factor out hardcoded loop limits min and max,
- handle compilation failure using require, and
- avoid using . in regexp to match $, {} and <>.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>