Add lowmem option and settings

Author: shoo

views/package_format_json.dt

@@ -583,6 +583,10 @@ block body
 			td "betterC"
 			td Compile in betterC mode
 			td -betterC
+		tr
+			td "lowmem"
+			td Enable the garbage collector for the compiler(dmd/ldc), reducing the compiler memory requirements but increasing compile times.
+			td -lowmem
 
 	h3#environment-variables Environment variables
 	include inc.package_format.envvars

views/package_format_sdl.dt

@@ -566,6 +566,10 @@ block body
 			td "betterC"
 			td Compile in betterC mode
 			td -betterC
+		tr
+			td "lowmem"
+			td Enable the garbage collector for the compiler(dmd/ldc), reducing the compiler memory requirements but increasing compile times.
+			td -lowmem
 
 	h3#environment-variables Environment variables
 	include inc.package_format.envvars

views/settings.dt

@@ -75,4 +75,9 @@ block body
 		tr
 			td defaultArchitecture
 			td: code string
-			td Force a different architecture (e.g. x86 or x86_64) 
+			td Force a different architecture (e.g. x86 or x86_64) 
+
+		tr
+			td defaultLowMemory
+			td: code bool
+			td Enable the garbage collector for the compiler(dmd/ldc), reducing the compiler memory requirements but increasing compile times.