gcc: enable -O2 compilation

To enable -O2 compilation we have to disable some optimizations:

- strict-aliasing (TODO: introduce required unions to enable this)
- aggressive-loop-optimizations
- array-bounds

Affected builds are

- sys/src/cmd/dossrv/build.json
- sys/src/cmd/ip/build.json
- sys/src/lib/authsrv/build.json
- sys/src/lib/memdraw/build.json

sys/src/cmd/dossrv/build.json

@@ -3,6 +3,10 @@
 		"Include": [
 			"../cmd.json"
 		],
+		"Cflags": [
+			"-fno-aggressive-loop-optimizations",
+			"-Wno-array-bounds"
+		],
 		"Install": "/arch/$ARCH/cmd/",
 		"Program": "dossrv",
 		"SourceFiles": [

sys/src/cmd/ip/build.json

@@ -3,6 +3,9 @@
 		"Include": [
 			"/sys/src/cmd/cmd.json"
 		],
+		"Cflags": [
+			"-fno-strict-aliasing"
+		],
 		"Install": "/arch/$ARCH/cmd/ip",
 		"Projects": [
 			"dhcpd/dhcpd.json",

sys/src/lib/authsrv/build.json

@@ -3,6 +3,9 @@
 		"Include": [
 			"../lib.json"
 		],
+		"Cflags": [
+			"-fno-strict-aliasing"
+		],
 		"Install": "/arch/$ARCH/lib/",
 		"Library": "libauthsrv.a",
 		"SourceFiles": [

sys/src/lib/memdraw/build.json

@@ -3,6 +3,9 @@
 		"Include": [
 			"../lib.json"
 		],
+		"Cflags": [
+			"-fno-strict-aliasing"
+		],
 		"Install": "/arch/$ARCH/lib/",
 		"Library": "libmemdraw.a",
 		"SourceFiles": [