[gdb/testsuite] Fix mi-sym-info.exp matching FAILs (2)

[gdb/testsuite] Fix mi-sym-info.exp matching FAILs (2)

With debug info packages for system libraries installed, I currently run into
some "internal buffer is full" errors with test-case gdb.mi/mi-sym-info.exp,
but if I disable the corresponding tests, I get further-on:
...
FAIL: gdb.mi/mi-sym-info.exp: List all functions matching pattern f3 \
  (unexpected output)
FAIL: gdb.mi/mi-sym-info.exp: List all functions matching type void \
  (unexpected output)
FAIL: gdb.mi/mi-sym-info.exp: List all variables matching type float \
  (unexpected output)
FAIL: gdb.mi/mi-sym-info.exp: -symbol-info-functions --max-results 1 \
  (unexpected output)
FAIL: gdb.mi/mi-sym-info.exp: -symbol-info-functions --max-results 2 \
  (unexpected output)
...

Fix this by making the matching more precise.

Tested on x86_64-linux.

Also tested with an extra:
...
mi_gdb_test "set debug-file-directory"
...
to prevent gdb from finding the debug info for system libraries.

gdb/testsuite/ChangeLog:

2020-03-13  Tom de Vries  <tdevries@suse.de>

	* gdb.mi/mi-sym-info.exp: Make matching more precise.