[PATCH] [RFC] Use llvm-symbolizer to symbolize LLVM/Clang crash dumps

[Ed Maste]

It appears this breaks the build on FreeBSD

```
In file included from ../lib/Support/Signals.cpp:30:
../lib/Support/Unix/Signals.inc:290:11: error: unknown type name 'ElfW'
    const ElfW(Phdr) *phdr = &info->dlpi_phdr[i];
          ^
../lib/Support/Unix/Signals.inc:290:21: error: expected ';' at end of declaration
    const ElfW(Phdr) *phdr = &info->dlpi_phdr[i];
                    ^
                    ;
../lib/Support/Unix/Signals.inc:291:9: error: use of undeclared identifier 'phdr'; did you mean 'Phdr'?
    if (phdr->p_type != PT_LOAD)
        ^~~~
        Phdr
../lib/Support/Unix/Signals.inc:290:16: note: 'Phdr' declared here
    const ElfW(Phdr) *phdr = &info->dlpi_phdr[i];
               ^
../lib/Support/Unix/Signals.inc:293:38: error: use of undeclared identifier 'phdr'; did you mean 'Phdr'?
    intptr_t beg = info->dlpi_addr + phdr->p_vaddr;
                                     ^~~~
                                     Phdr
../lib/Support/Unix/Signals.inc:290:16: note: 'Phdr' declared here
    const ElfW(Phdr) *phdr = &info->dlpi_phdr[i];
               ^
../lib/Support/Unix/Signals.inc:294:26: error: use of undeclared identifier 'phdr'; did you mean 'Phdr'?
    intptr_t end = beg + phdr->p_memsz;
                         ^~~~
                         Phdr
../lib/Support/Unix/Signals.inc:290:16: note: 'Phdr' declared here
    const ElfW(Phdr) *phdr = &info->dlpi_phdr[i];
               ^
../lib/Support/Unix/Signals.inc:372:23: warning: unused variable 'Err' [-Wunused-variable]
  if (std::error_code Err = OutputBuf.getError())
                      ^
1 warning and 5 errors generated.
```

http://reviews.llvm.org/D5610