* add `@compileLog(...)` builtin function
- Helps debug code running at compile time
- See #240
* fix crash when there is an error on the start value of a slice
* add implicit cast from int and float types to int and float
literals if the value is known at compile time
* make array concatenation work with slices in addition to
arrays and c string literals
* fix compile error message for something not having field access
* fix crash when `@setDebugSafety()` was called from a
function being evaluated at compile-time
* fix compile-time evaluation of overflow math builtins.
* avoid debug safety panic handler in builtin.o and compiler_rt.o
since we use no debug safety in these modules anyway
* add compiler_rt functions for division on ARM
- Closes#254
* move default panic handler to std.debug so users can
call it manually
* std.io.printf supports a width in the format specifier
* instead of emitting a breakpoint for a debug safety crash,
zig calls a panic function which prints an error message
and a stack trace and then calls abort.
* on freestanding OS, this panic function has a default
implementation of a simple infinite loop.
* users can override the panic implementation by providing
`pub fn panic(message: []const u8) -> unreachable { }`
* workaround for LLVM segfaulting when you try to use cold
calling convention on ARM.
closes#245
