Rollup merge of #77950 - arlosi:sha256, r=eddyb

Add support for SHA256 source file hashing

Adds support for `-Z src-hash-algorithm sha256`, which became available in LLVM 11.

Using an older version of LLVM will cause an error `invalid checksum kind` if the hash algorithm is set to sha256.

r? `@eddyb`
cc #70401 `@est31`

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -801,6 +801,7 @@ fn file_metadata_raw(
                     let kind = match hash.kind {
                         rustc_span::SourceFileHashAlgorithm::Md5 => llvm::ChecksumKind::MD5,
                         rustc_span::SourceFileHashAlgorithm::Sha1 => llvm::ChecksumKind::SHA1,
+                        rustc_span::SourceFileHashAlgorithm::Sha256 => llvm::ChecksumKind::SHA256,
                     };
                     (kind, hex_encode(hash.hash_bytes()))
                 }