[llvm] [llvm-lit][test] Precommit tests for lit's built-in cat command (PR #101530)

[James Henderson via llvm-commits]

================
@@ -0,0 +1,50 @@
+## C Program to generate all ASCII characters in allchars
+# #include <stdio.h>
+# int main() {
+#     FILE *fptr = fopen("allchars.txt", "w");
+#     if(fptr == NULL) {
+#         return 1;
+#     }
+#     for(int i = 0; i < 256; i++) {
+#         fprintf(fptr, "%c", i);
+#     }
+#     fclose(fptr);
+#     return 0;
+# }
+
+## Tests to check cat -v output
----------------
jh7370 wrote:

Similar to my comment for the -e case, I think it would be useful to include a brief description of what the -v output actually means.

https://github.com/llvm/llvm-project/pull/101530