This change adds a manual override to control building of the ptrace
library, similar to the existing --enable-coredump option. The
default is set based on the existence of sys/ptrace.h, allowing it
to be automatically disabled for platforms that do not have ptrace.
Add support for the 32bit SuperH architecture running Linux.
Specifically, support is added for SH4, and support for earlier SH
versions and to the 64bit SH5 are left out. This was tested in qemu with
a little-endian SH4 debian image & GCC 4.7 cross compiler.
Add MIPS support to the coredump library. Explicit support for the MIPS
program counter register is added so that we can start backtracing from
the program counter value we read from a core dump. The PC register
support was not strictly required for local backtracing, and we will in
fact just plug the return address to the PC register in getcontext().
I have only tested the 32bit "OABI" paths.
We do not really need to care if the system provides `backtrace()',
since we will want to test the one provided in libunwind, not the one
that is provided by the system. The `backtrace()' calls should already
be aliased to `unw_backtrace()', but if that is not working for whatever
reason, we can call `unw_backtrace()' explicitly.
We can use the __sync builtin atomics also on other architectures than
IA64. GCC 4.7 documentation notes that these builtins are ``legacy'' --
adding support for the newer GCC __atomic atomics should be fairly easy.
