Fix Linux build: add _DEFAULT_SOURCE for endian macros

-std=c11 disables _DEFAULT_SOURCE on glibc, hiding le16toh/be16toh
from <endian.h>. Add -D_DEFAULT_SOURCE to CGo CFLAGS.

Author: DeusData

internal/cbm/cbm.go

@@ -1,7 +1,7 @@
 package cbm
 
 /*
-#cgo CFLAGS: -std=c11 -O2 -Wall -Ivendored/ts_runtime/include
+#cgo CFLAGS: -std=c11 -D_DEFAULT_SOURCE -O2 -Wall -Ivendored/ts_runtime/include
 #include "cbm.h"
 #include "helpers.h"
 #include "lang_specs.h"