Add -lm to the default libs for Linux & Darwin

libm is a default library for device builds, so default it for host
builds as well.

Also removes duplicate additions of -ldl, -lpthread, -lm and -lrt.

Test: m host
Change-Id: I8f7e799d48a1f427e48dcfb1d0ccba93c5f9780b

cc/linker.go

@@ -211,11 +211,12 @@ func (linker *baseLinker) linkerFlags(ctx ModuleContext, flags Flags) Flags {
 			flags.LdFlags = append(flags.LdFlags, linker.Properties.Host_ldlibs...)
 
 			if !ctx.Windows() {
-				// Add -ldl, -lpthread and -lrt to host builds to match the default behavior of device
+				// Add -ldl, -lpthread, -lm and -lrt to host builds to match the default behavior of device
 				// builds
 				flags.LdFlags = append(flags.LdFlags,
 					"-ldl",
 					"-lpthread",
+					"-lm",
 				)
 				if !ctx.Darwin() {
 					flags.LdFlags = append(flags.LdFlags, "-lrt")