Add fmtmsg

tests/fmtmsg.c

@@ -0,0 +1,39 @@
+#include <fmtmsg.h>
+#include <unistd.h>
+int main() {
+    /* Returned Value
+     * MM_OK: 0 - The function succeeded.
+     * MM_NOCON: 4 - The function was unable to generate a console message, but otherwise succeeded.
+     * MM_NOMSG: 1 - The function was unable to generate a message on standard error, but otherwise succeeded.
+     * MM_NOTOK: -1 - The function failed completely.
+     * 
+     * Take from: https://www.ibm.com/docs/en/zos/3.1.0?topic=functions-fmtmsg-display-message-in-specified-format
+     */
+    int mm_ok = fmtmsg(MM_PRINT, "XSI:cat", MM_ERROR, "illegal option",
+    "refer to cat in user's reference manual", "XSI:cat:001");
+    if (mm_ok != 0) {
+        return -1;
+    }
+    // Thats return 0 in glibc but return 4 in musl
+    // So we expect 4 here
+    int mm_nocon = fmtmsg(MM_PRINT | MM_CONSOLE, "XSI:cat", MM_ERROR, "illegal option",
+    "refer to cat in user's reference manual", "XSI:cat:001");
+    if (mm_nocon != MM_NOCON) {
+        return -1;
+    }
+    //We close stderr to test.
+    close(STDERR_FILENO);
+    int mm_nomsg = fmtmsg(MM_PRINT , "XSI:cat", MM_ERROR, "illegal option",
+    "refer to cat in user's reference manual", "XSI:cat:001");
+    if (mm_nomsg != MM_NOMSG) {
+        return -1;
+    }
+    // Thats return 1 in glibc but return -1 in musl
+    // Soo we expect -1 here
+    int mm_notok = fmtmsg(MM_PRINT | MM_CONSOLE, "XSI:cat", MM_ERROR, "illegal option",
+    "refer to cat in user's reference manual", "XSI:cat:001");
+    if (mm_notok != MM_NOTOK) {
+        return -1;
+    }
+    return 0;    
+}