Make lldb -Werror clean for -Wstring-conversion

Also found/fixed one bug identified by this warning in
RenderScriptx86ABIFixups.cpp where a string literal was being used in an
effort to provide a name for an instruction/register, but was instead
being passed as the bool 'isVolatile' parameter.

llvm-svn: 291198
diff --git a/lldb/tools/driver/Platform.cpp b/lldb/tools/driver/Platform.cpp
index 1a58d4d..a9d1bee 100644
--- a/lldb/tools/driver/Platform.cpp
+++ b/lldb/tools/driver/Platform.cpp
@@ -34,9 +34,8 @@
     return 0;
   } break;
   default:
-    assert(!"Not implemented!");
+    llvm_unreachable("Not implemented!");
   }
-  return -1;
 }
 
 int kill(pid_t pid, int sig) {
@@ -44,13 +43,11 @@
   if (pid == getpid())
     exit(sig);
   //
-  assert(!"Not implemented!");
-  return -1;
+  llvm_unreachable("Not implemented!");
 }
 
 int tcsetattr(int fd, int optional_actions, const struct termios *termios_p) {
-  assert(!"Not implemented!");
-  return -1;
+  llvm_unreachable("Not implemented!");
 }
 
 int tcgetattr(int fildes, struct termios *termios_p) {