transpile: Add snapshot test for main function

Author: Rua

c2rust-transpile/tests/snapshots/main.c

@@ -0,0 +1,3 @@
+int main(int argc, char **argv, char **envp) {
+    return 0;
+}

c2rust-transpile/tests/snapshots/[email protected]

@@ -0,0 +1,50 @@
+---
+source: c2rust-transpile/tests/snapshots.rs
+expression: cat tests/snapshots/main.rs
+input_file: c2rust-transpile/tests/snapshots/main.c
+---
+#![allow(
+    dead_code,
+    non_camel_case_types,
+    non_snake_case,
+    non_upper_case_globals,
+    unused_assignments,
+    unused_mut
+)]
+unsafe fn main_0(
+    mut argc: ::core::ffi::c_int,
+    mut argv: *mut *mut ::core::ffi::c_char,
+    mut envp: *mut *mut ::core::ffi::c_char,
+) -> ::core::ffi::c_int {
+    return 0 as ::core::ffi::c_int;
+}
+pub fn main() {
+    let mut args: Vec<*mut ::core::ffi::c_char> = Vec::new();
+    for arg in ::std::env::args() {
+        args.push(
+            ::std::ffi::CString::new(arg)
+                .expect("Failed to convert argument into CString.")
+                .into_raw(),
+        );
+    }
+    args.push(::core::ptr::null_mut());
+    let mut vars: Vec<*mut ::core::ffi::c_char> = Vec::new();
+    for (var_name, var_value) in ::std::env::vars() {
+        let var: String = format!("{}={}", var_name, var_value);
+        vars.push(
+            ::std::ffi::CString::new(var)
+                .expect("Failed to convert environment variable into CString.")
+                .into_raw(),
+        );
+    }
+    vars.push(::core::ptr::null_mut());
+    unsafe {
+        ::std::process::exit(
+            main_0(
+                (args.len() - 1) as ::core::ffi::c_int,
+                args.as_mut_ptr() as *mut *mut ::core::ffi::c_char,
+                vars.as_mut_ptr() as *mut *mut ::core::ffi::c_char,
+            ) as i32,
+        )
+    }
+}