inspect stack during error reporting

We already inspect the registers during error reporting, but some important pointers may be only on stack, especially on architectures which don't have so many registers.
Since hs_err files are often all we get after a crash, it is often valuable to spend a little space for more information about what's referenced on top of the stack.

This feature inspects the content of 8 stack slots of the top of the stack. The new section "Stack slot to memory mapping" shows up in hs_err files when a context is given and the output looks like the following example:

Stack slot to memory mapping:
stack at sp + 0 slots: 0xffffffff7b3b5c24: ucrypto_digest_final+0 in /lib/sparcv9/libucrypto.so.1 at 0xffffffff7b300000
stack at sp + 1 slots: 0x0000000100df6b50 points into unknown readable memory: 00 00 00 00 00 00 00 00
stack at sp + 2 slots: 0x0000000000000003 is an unknown value
stack at sp + 3 slots: 0xffffffff06a05bf0: _GLOBAL_OFFSET_TABLE_+0 in /jvm_12/lib/libj2ucrypto.so at 0xffffffff06900000
stack at sp + 4 slots: 0xffffffff7f18b7a8: __malloc_lock+0x18 in /lib/sparcv9/libc.so.1 at 0xffffffff7ef00000
stack at sp + 5 slots: 0xffffffff06a05f48: _PROCEDURE_LINKAGE_TABLE_+0x348 in /jvm_12/lib/libj2ucrypto.so at 0xffffffff06900000
stack at sp + 6 slots: 0x0 is NULL
stack at sp + 7 slots: 0x0000000100df6b50 points into unknown readable memory: 00 00 00 00 00 00 00 00