Fix flags for dev build (#31955)

Fix the flags used when the environmet varialbe DEV=true is set. This
allows to generate binaries without code optmisation and debug
symbols.

Co-authored-by: Craig MacKenzie <craig.mackenzie@elastic.co>

CHANGELOG-developer.next.asciidoc

@@ -75,6 +75,7 @@ The list below covers the major changes between 7.0.0-rc2 and main only.
 - Avoid panicking in `add_fields` processor when input event.Fields is a nil map. {pull}28219[28219]
 - Drop event batch when get HTTP status 413 from Elasticsearch to avoid infinite loop {issue}14350[14350] {pull}29368[29368]
 - Allow to use metricbeat for named mssql instances. {issue}24076[24076] {pull}30859[30859]
+- Setting DEV=true when running `mage build` now correctly generates binaries without optimisations and with debug symbols {pull}31955[31955]
 
 ==== Added
 

dev-tools/mage/build.go

@@ -67,7 +67,7 @@ func DefaultBuildArgs() BuildArgs {
 
 	if DevBuild {
 		// Disable optimizations (-N) and inlining (-l) for debugging.
-		args.ExtraFlags = append(args.ExtraFlags, `-gcflags`, `"all=-N -l"`)
+		args.ExtraFlags = append(args.ExtraFlags, `-gcflags=all=-N -l`)
 	} else {
 		// Strip all debug symbols from binary (does not affect Go stack traces).
 		args.LDFlags = append(args.LDFlags, "-s")