Fix the Mac OS X 10.8 and 10.9 builds.

This adds a PL_MIN_MACOSX_SDK project setting that is used to define the
minimum supported Mac OS X SDK; we'll continue to support building on
10.8, where various ARM64 defines are unavailable.

Once this is bumped to 10.9 -- or 10.8 SDK is updated to include
the ARM64 CPU types -- the replacement ARM #defines will trigger
compilation errors.

In addition, this commit also makes testing of objc_debug_isa_class_mask
conditional on __arm64__; the symbol is not exported on other
architectures.
Rename PLCrashConstants.h to the more apt PLCrashMacros.h.
Quiesce -Wtautological-constant-out-of-range-compare warning.
Fix explicit typing of the plcrash_dwarf_cfa_reg_rule_t rule value.

This fixes a -Wtautological-constant-out-of-range-compare reported
issue.
Implement a clang-425.0.28-compatible work-around for -Wtautological-constant-out-of-range-compare.

In these particular cases, the point of the check is to document that
the issue has been (and in the future, should be) considered. The fact
that the cases are evaluated as tautological true is the point.

Specifying -Wno-tautological-constant-out-of-range-compare for the
entire project will break versions of clang that do not support the
warning flag (such as clang-425.0.28, shipped with Xcode 4). By using
the verbose pragma syntax, we can enable -Wno-unknown-pragmas for just
the code in question, which will allow clang to ignore subsequent the
'-Wtautological-constant-out-of-range-compare' flag if unknown.

This commit also adds a PLCR_PRAGMA_CLANG macro to enable/disable
clang-specific pragmas depending on the host compiler; the aim is to
keep the DWARF code modified here non-specific to clang.
Fix build on Xcode 4 when project path contains a space.

Issue: PLCR-497
Submitted by: Daniel Jalkut
Minor Modifications: Landon Fuller
Explicitly write the Mach server implementation to /dev/null; this matches Xcode's MIG target behavior.

Issue: PLCR-497
Bump the version number for 1.2-beta2.
Fix use of TARGET_OS_MAC; iOS also enables this.
Standardize on 64-bit register width; this matches the x86 implementation.

This permits crash reporting on arm64 processes from arm32 host process;
not something we'll need, but it also has the side-benefit of quiescing
a spurious clang tautological comparison warning.
Enable x86-64 builds for the Simulator targets.
Remove the simulator's 'run test' build phase.

In Xcode 5, the standard debug messages that fire when testing error
conditions are all treated as errors when they occur during the build
process.

We'll need to switch over to XCTest eventually, but in the meantime,
this replaces the complex instantiation of the unit tests within the
simulator, and instead matches the behavior to that of the device
tests, where we simply launch the test application directly.
Merge branch 'master' into landonf-PLCR-499-armv8-unwinding