Revert "runtime: cleanup free_memory comptime conditional (#18968)"

This reverts commit 571469a.

vlib/runtime/free_memory_impl_darwin.c.v

@@ -19,13 +19,16 @@ fn C.host_page_size(host C.host_t, out_page_size &C.vm_size_t) int
 fn C.host_statistics64(host C.host_t, flavor int, host_info_out &int, host_info_outCnt &u32) int
 
 fn free_memory_impl() usize {
-	mut hs := C.vm_statistics64_data_t{}
-	mut vmsz := u32(C.HOST_VM_INFO64_COUNT)
-	mut hps := u32(0)
-	mut host := C.mach_host_self()
-	unsafe {
-		C.host_statistics64(host, C.HOST_VM_INFO64, &int(&hs), &vmsz)
-		C.host_page_size(host, &C.vm_size_t(&hps))
+	$if macos {
+		mut hs := C.vm_statistics64_data_t{}
+		mut vmsz := u32(C.HOST_VM_INFO64_COUNT)
+		mut hps := u32(0)
+		mut host := C.mach_host_self()
+		unsafe {
+			C.host_statistics64(host, C.HOST_VM_INFO64, &int(&hs), &vmsz)
+			C.host_page_size(host, &C.vm_size_t(&hps))
+		}
+		return usize(u64(hs.free_count) * u64(hps))
 	}
-	return usize(u64(hs.free_count) * u64(hps))
+	return 1
 }

vlib/runtime/free_memory_impl_linux.c.v

@@ -1,7 +1,10 @@
 module runtime
 
 fn free_memory_impl() usize {
-	page_size := usize(C.sysconf(C._SC_PAGESIZE))
-	av_phys_pages := usize(C.sysconf(C._SC_AVPHYS_PAGES))
-	return page_size * av_phys_pages
+	$if linux {
+		page_size := usize(C.sysconf(C._SC_PAGESIZE))
+		av_phys_pages := usize(C.sysconf(C._SC_AVPHYS_PAGES))
+		return page_size * av_phys_pages
+	}
+	return 1
 }