[gdb/testsuite] Fix gdb.base/style.exp on freebsd

[gdb/testsuite] Fix gdb.base/style.exp on freebsd

On x86_64-freebsd, with test-case gdb.base/style.exp I run into:
...
(gdb) print $_colorsupport
\e[36;49;22;27m$1\e[m = "monochrome"
(gdb) FAIL: $exp: colorsupport_8color: color support is 8 color
...

Fix this by applying the same fix as for tuiterm: use TERM=ansiw instead of
TERM=ansi for bsd, getting us instead:
...
(gdb) print $_colorsupport
\e[36;49;22;27m$1\e[m = "monochrome,ansi_8color"
(gdb) PASS: $exp: colorsupport_8color: color support is 8 color
...

Tested on x86_64-freebsd.