[Sanitizers] Fix sanitizer_linux_libcdep.cc compilation on Solaris

[ro]

Summary

Both LLVM 8.0.0 and current trunk fail to compile on Solaris 11/x86 with GCC 8.1.0:

/vol/llvm/src/llvm/dist/projects/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc: In function ‘void __sanitizer::ReExec()’:
/vol/llvm/src/llvm/dist/projects/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc:831:14: error: ‘getexecname’ was not declared in this scope
   pathname = getexecname();
              ^~~~~~~~~~~
/vol/llvm/src/llvm/dist/projects/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cc:831:14: note: suggested alternative: ‘gethostname’
   pathname = getexecname();
              ^~~~~~~~~~~
              gethostname

This is easily fixed by including `<stdlib.h>` which declares that function. With that
patch, compilation continues.

[ro]

Ping. Another Solaris-specific patch which might be considered obvious?

[eugenis]

LGTM

compiler-rt/trunk/lib/sanitizer_common/sanitizer_linux_libcdep.cc

 #endif
 
 #if SANITIZER_NETBSD
 #include <sys/sysctl.h>
 #include <sys/tls.h>
 #endif
 
 #if SANITIZER_SOLARIS
+#include <stdlib.h>
 #include <thread.h>
 #endif
 
 #if SANITIZER_ANDROID
 #include <android/api-level.h>
 #if !defined(CPU_COUNT) && !defined(__aarch64__)
 #include <dirent.h>
 #include <fcntl.h>