Harden gdb.base/bp-permanent.exp

Harden gdb.base/bp-permanent.exp

This testcase does not work as expected in QEMU (aarch64 QEMU in my case). It
fails when trying to manually write the breakpoint instruction to a certain
PC address.

(gdb) p /x addr_bp[0] = buffer[0]^M
Cannot access memory at address 0x400834^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, sw_watchpoint=0: setup: p /x addr_bp[0] = buffer[0]
p /x addr_bp[1] = buffer[1]^M
Cannot access memory at address 0x400835^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, sw_watchpoint=0: setup: p /x addr_bp[1] = buffer[1]
p /x addr_bp[2] = buffer[2]^M
Cannot access memory at address 0x400836^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, sw_watchpoint=0: setup: p /x addr_bp[2] = buffer[2]
p /x addr_bp[3] = buffer[3]^M
Cannot access memory at address 0x400837^M
(gdb) PASS: gdb.base/bp-permanent.exp: always_inserted=off, sw_watchpoint=0: setup: p /x addr_bp[3] = buffer[3]

The following patch prevents a number of failures by detecting this and bailing out in case the target has such a restriction. Writing to .text from within the program isn't any better. It just leads to a SIGSEGV.

Before the patch:

                === gdb Summary ===

After the patch:

                === gdb Summary ===

gdb/testsuite/ChangeLog:
2015-04-13  Luis Machado  <lgustavo@codesourcery.com>

	* gdb.base/bp-permanent.exp (test): Handle the case of being unable
	to write to the .text section.