Initial support for the Clang compiler and numerous warning fixes

indra/llcommon/llhash.h

@@ -39,6 +39,7 @@
 #include <hash_map>
 #include <algorithm>
 #elif LL_DARWIN || LL_LINUX
+#if CC_GCC
 #  if GCC_VERSION >= 40300 // gcc 4.3 and up
 #    include <backward/hashtable.h>
 #  elif GCC_VERSION >= 30400 // gcc 3.4 and up
@@ -48,6 +49,9 @@
 #  else
 #    include <hashtable.h>
 #  endif
+#elif CC_CLANG
+#  include <hashtable.h>
+#endif
 #elif LL_SOLARIS
 #include <ext/hashtable.h>
 #else