intel/compiler tests: fix variable type for getopt_long() return value

`getopt_long()` returns an `int`, not a `char`; putting the value in
a `char` before comparing it to `-1` was making the comparison always
fail, resulting in the invalid codepath taken that then fails with:

    option `-' is invalid: ignored

cc: mesa-stable

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34756>

src/intel/compiler/brw_asm_tool.c

@@ -132,7 +132,7 @@ int main(int argc, char **argv)
    void *mem_ctx = ralloc_context(NULL);
    FILE *input_file = NULL;
    char *output_file = NULL;
-   char c;
+   int c;
    FILE *output = stdout;
    bool help = false, compact = false;
    uint64_t pci_id = 0;

src/intel/compiler/elk/elk_asm_tool.c

@@ -208,7 +208,7 @@ i965_postprocess_labels()
 int main(int argc, char **argv)
 {
    char *output_file = NULL;
-   char c;
+   int c;
    FILE *output = stdout;
    bool help = false, compact = false;
    void *store;