arm: Tune default architecture target

We lost these tunings when I moved us away from board focused
builds. I feel like most of our ARM interest is around ARMv7+

Change-Id: Ie301d275a74d48ee3d0c4c7dc7d6cdd635288a7b

build/jam/ArchitectureRules

@@ -49,7 +49,14 @@ rule ArchitectureSetup architecture
 			-Wno-cast-align -Wno-gnu-designator ;
 	}
 
+	# default architecture tuning
+	# TODO: Do we want x86_gcc2 -march=pentium here?
 	local cpu = $(HAIKU_CPU_$(architecture)) ;
+	switch $(cpu) {
+		case arm :
+			ccBaseFlags += -march=armv7-a -mfloat-abi=hard ;
+	}
+
 	if $(cpu) = arm {
 		if $(HAIKU_CC_IS_CLANG_$(architecture)) != 1 {
 			# For stackcrawls - not supported by Clang