Add riscv vxworks target specific constants

Author: biabbas

src/vxworks/riscv32.rs

@@ -0,0 +1,4 @@
+pub type c_char = i8;
+pub type wchar_t = i32;
+pub type c_long = i32;
+pub type c_ulong = u32;

src/vxworks/riscv64.rs

@@ -0,0 +1,4 @@
+pub type c_char = u8;
+pub type wchar_t = u32;
+pub type c_long = i64;
+pub type c_ulong = u64;