[gdb/testsuite, tclint] Fix gdb.testsuite

[gdb/testsuite, tclint] Fix gdb.testsuite

Running tclint on the test-cases in gdb.testsuite shows a few problems:
...
board-sanity.exp:47:38: line has trailing whitespace [trailing-whitespace]
board-sanity.exp:83:1: line has trailing whitespace [trailing-whitespace]
board-sanity.exp:95:38: line has trailing whitespace [trailing-whitespace]
gdb-caching-proc-consistency.exp:66:2: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
gdb-caching-proc-consistency.exp:117:12: eval received an argument with a \
  substitution, unable to parse its arguments [command-args]
with-override.exp:53:18: expression with substitutions should be enclosed by \
  braces [unbraced-expr]
with-override.exp:57:18: expression with substitutions should be enclosed by \
  braces [unbraced-expr]
...

Fix these.

Tested on x86_64-linux.