OverriddenJamRules: sort out build flags for .S files

Change-Id: I1ad67e1aab3911e7b66dc801923e8ba5cc1e087d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4755
Reviewed-by: waddlesplash <[email protected]>
Tested-by: Commit checker robot <[email protected]>

build/jam/OverriddenJamRules

@@ -173,12 +173,16 @@ rule Object
 
 rule As
 {
+	Depends $(<) : $(>) [ on $(1) return $(PLATFORM) ] ;
+
+	on $(1) {
 		local flags ;
 		local includesSeparator ;
 		local localIncludesOption ;
 		local systemIncludesOption ;
-	if [ on $(1) return $(PLATFORM) ] = host {
+
-		flags = [ on $(1) return $(HOST_ASFLAGS) $(ASFLAGS) ] ;
+		if $(PLATFORM) = host {
+			flags = $(HOST_ASFLAGS) $(ASFLAGS) ;
 
 			CC on $(1) = $(HOST_CC) ;
 
@@ -186,8 +190,7 @@ rule As
 			localIncludesOption = $(HOST_LOCAL_INCLUDES_OPTION) ;
 			systemIncludesOption = $(HOST_SYSTEM_INCLUDES_OPTION) ;
 		} else {
-		flags = [ on $(1) return $(TARGET_ASFLAGS_$(TARGET_PACKAGING_ARCH))
+			flags = $(TARGET_ASFLAGS_$(TARGET_PACKAGING_ARCH)) $(ASFLAGS) ;
-			$(ASFLAGS) ] ;
 
 			CC on $(1) = $(TARGET_CC_$(TARGET_PACKAGING_ARCH)) ;
 
@@ -199,13 +202,13 @@ rule As
 				= $(TARGET_SYSTEM_INCLUDES_OPTION_$(TARGET_PACKAGING_ARCH)) ;
 		}
 
-	Depends $(<) : $(>) [ on $(1) return $(PLATFORM) ] ;
 		ASFLAGS on $(<) += $(flags) $(SUBDIRASFLAGS) ;
 		ASHDRS on $(<) = [ on $(<) FIncludes $(HDRS) : $(localIncludesOption) ]
 			$(includesSeparator)
 			[ on $(<) FSysIncludes $(SYSHDRS) : $(systemIncludesOption) ] ;
 		ASDEFS on $(<) = [ on $(<) FDefines $(DEFINES) ] ;
 	}
+}
 
 actions As
 {