libutil: remove warnOnce macro

it's only used once, and even that one use is highly questionable. more
instances of warnOnce should be much more principled than this has been

Change-Id: I5856570c99cb44462e700d753d0c706a5db03c4b

src/libmain/shared.cc

@@ -33,9 +33,13 @@ void printGCWarning()
 {
     if (!gcWarning) return;
     static bool haveWarned = false;
-    warnOnce(haveWarned,
+    if (!haveWarned) {
+        haveWarned = true;
+        warn(
             "you did not specify '--add-root'; "
-        "the result might be removed by the garbage collector");
+            "the result might be removed by the garbage collector"
+        );
+    }
 }
 
 

src/libutil/logging.hh

@@ -283,12 +283,6 @@ inline void warn(const std::string & fs, const Args & ... args)
     logger->warn(HintFmt(fs, args...).str());
 }
 
-#define warnOnce(haveWarned, args...) \
-    if (!haveWarned) {                \
-        haveWarned = true;            \
-        warn(args);                   \
-    }
-
 void writeToStderr(std::string_view s);
 
 }