Literal strings are located in read-only memory and should be "const
char*". "gcc -Wwrite-strings" warns when using non-const literal
strings with messages like:
libqpol/policy_parse.y: In function 'yyparse':
libqpol/policy_parse.y:381:21: warning: passing argument 1 of
'insert_id' discards 'const' qualifier from pointer target type
{ if (insert_id("T",0)) return -1; }
^
Fix these warnings by using "const char*" instead of "char*" for some
function parameters.
This makes gcc report other warnings about hashtab_search (from
libsepol). This function incorrectly defines its second parameter as
"char *const key" instead of "const char* key" (this fact is hidden
behind hashtab_key_t typedef).
