bugfix: add missing ":" to errExit message

Use `Error: ` instead of just `Error `, for consistency with the other
error messages.

This amends commit f7da0e7 ("build: move errExit macro into inline
function", 2024-01-29) / PR netblue30#6217.

Misc: This was noticed on netblue30#6705.

Author: kmk3

src/include/common.h

@@ -44,7 +44,7 @@
 static inline void __attribute__((noreturn))
 _errExit(const char *fname, int lineno, const char *func, const char *msg) {
 	char msgout[500];
-	snprintf(msgout, 500, "Error %s:%d: %s: %s", fname, lineno, func, msg);
+	snprintf(msgout, 500, "Error: %s:%d: %s: %s", fname, lineno, func, msg);
 	perror(msgout);
 	exit(1);
 }