Use software watchpoints if hardware watchpoints are not available when testing gdb...

Use software watchpoints if hardware watchpoints are not available when testing gdb.base/watch-bitfields.exp

There are targets GDB thinks support hardware watchpoints, but in reality they
don't.  Though it may seem that hardware watchpoint creation was successful,
the actual insertion of such watchpoint will fail when GDB moves the inferior.

(gdb) watch -location q.a^M
Hardware watchpoint 2: -location q.a^M
(gdb) PASS: gdb.base/watch-bitfields.exp: -location watch against bitfields: watch -location q.a
watch -location q.e^M
Hardware watchpoint 3: -location q.e^M
(gdb) PASS: gdb.base/watch-bitfields.exp: -location watch against bitfields: watch -location q.e
print q.a^M
$1 = 0^M
(gdb) PASS: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.a: 0->1: print expression before
continue^M
Continuing.^M
Warning:^M
Could not insert hardware watchpoint 2.^M
Could not insert hardware watchpoint 3.^M
Could not insert hardware breakpoints:^M
You may have requested too many hardware breakpoints/watchpoints.^M
^M
(gdb) FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.a: 0->1: continue

This leads to a number of FAILs:

FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.a: 0->1: continue
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.a: 0->1: print expression after
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.e: 0->5: continue
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.e: 0->5: print expression after
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.a: 1->0: print expression before
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.a: 1->0: continue
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.e: 5->4: print expression before
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.e: 5->4: continue
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: q.e: 5->4: print expression after
FAIL: gdb.base/watch-bitfields.exp: -location watch against bitfields: continue until exit
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 0->4: continue
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 0->4: print expression after
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 4->10: print expression before
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 4->10: continue
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 4->10: print expression after
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 10->3: print expression before
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 10->3: continue
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 10->3: print expression after
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 3->2: print expression before
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 3->2: continue
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 3->2: print expression after
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 2->1: print expression before
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 2->1: continue
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 2->1: print expression after
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 1->0: print expression before
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: q.d + q.f + q.g: 1->0: continue
FAIL: gdb.base/watch-bitfields.exp: regular watch against bitfields: continue until exit

We can avoid these errors/FAILs by checking the board data and switching to
software watchpoints if the board does not support hardware watchpoints.

gdb/testsuite/ChangeLog:

2015-04-29  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.base/watch-bitfields.exp: Switch to software watchpoints if
	the target does not support hardware watchpoints.