MIES_GlobalStringAndVariableAccess.ipf: fix return in mac code

The function `ExecuteGitForMIESVersion()` contained MacOSX specific code with an
invalid break statement. This one doesn't compile, because it wasn't used inside
a loop or switch statement and is now replaced with an abort according to the
function documentation.

Author: Garados007

Packages/MIES/MIES_GlobalStringAndVariableAccess.ipf

@@ -304,7 +304,7 @@ static Function ExecuteGitForMIESVersion(string gitPathOrName, string gitDir, st
 	if(V_flag)
 		printf "Missing functional git executable, please install the \"Xcode commandline tools\" via \"xcode-select --install\" in Terminal.\r"
 		ControlWindowToFront()
-		break
+		abort
 	endif
 
 	sprintf cmd, "do shell script \"%s --git-dir='%s' describe --always --tags --match 'Release_*' > '%sversion.txt' 2>&1\"", gitPathOrName, gitDir, topDir