Treat u8 literals by their element type (#492)

Pre C++-20 u8 literals were `const char*`, post C++-20 they are `const
char8_t*`

Author: lucic71

cpp2rust/converter/converter_lib.cpp

@@ -259,7 +259,7 @@ bool IsStringLiteralExpr(const clang::Expr *expr) {
 
 bool IsCodeUnitStringLiteral(const clang::StringLiteral *expr) {
   return expr->getCharByteWidth() != 1 ||
-         expr->getKind() == clang::StringLiteralKind::UTF8;
+         expr->getType()->getArrayElementTypeNoTypeQual()->isChar8Type();
 }
 
 bool IsUserDefinedDecl(const clang::Decl *decl) {

tests/unit/char_signed.cpp

@@ -19,6 +19,9 @@ int main() {
   printf("%d %d\n", lit[0], ulit[0]);
   printf("%d\n", is_negative(lit));
 
+  const char *u8s = u8"\u00e9";
+  printf("%d %d\n", u8s[0], u8s[1]);
+
   const char *p = "\x80";
   printf("%d %d\n", p[0], (unsigned char)p[0]);
 

tests/unit/out/refcount/char_signed.rs

@@ -32,6 +32,12 @@ fn main_0() -> i32 {
         "{}",
         (({ is_negative_1((lit.as_pointer() as Ptr::<i8>),) }) as i32)
     );
+    let mut u8s: Ptr<i8> = Ptr::<i8>::from_string_literal(b"\xc3\xa9");
+    println!(
+        "{} {}",
+        ((elem!(u8s, 0).read()) as i32),
+        ((elem!(u8s, 1).read()) as i32)
+    );
     let mut p: Ptr<i8> = Ptr::<i8>::from_string_literal(b"\x80");
     println!(
         "{} {}",

tests/unit/out/unsafe/char_signed.rs

@@ -38,6 +38,12 @@ unsafe fn main_0() -> i32 {
         c"%d\n".as_ptr() as *const i8,
         ((unsafe { is_negative_1((lit.as_mut_ptr()).cast_const()) }) as i32),
     );
+    let mut u8s: *const libc::c_char = c"\xc3\xa9".as_ptr();
+    printf(
+        c"%d %d\n".as_ptr() as *const i8,
+        ((*u8s.offset((0) as isize)) as i32),
+        ((*u8s.offset((1) as isize)) as i32),
+    );
     let mut p: *const libc::c_char = c"\x80".as_ptr();
     printf(
         c"%d %d\n".as_ptr() as *const i8,