Don't require flags that only disable warnings

These flags aren't strictly required, they're only used to prevent
warnings when compiling tree-sitter parsers.

Should help with compiling on MSVC, see #63.

CHANGELOG.md

@@ -14,6 +14,11 @@ When logging is enabled (e.g. `RUST_LOG=warn`), difftastic now warns
 on syntax errors. Difftastic is intended to be robust against syntax
 errors, so this is primarily intended for parser debugging.
 
+### Build
+
+Difftastic now requires fewer C compiler flags, so it should build in
+more environments (e.g. compiling with MSVC).
+
 ## 0.12
 
 ### Display

build.rs

@@ -28,9 +28,9 @@ impl TreeSitterParser {
                 .include(&dir)
                 .cpp(true)
                 .flag("--std=c++14")
-                .flag("-Wno-implicit-fallthrough")
-                .flag("-Wno-unused-parameter")
-                .flag("-Wno-ignored-qualifiers");
+                .flag_if_supported("-Wno-implicit-fallthrough")
+                .flag_if_supported("-Wno-unused-parameter")
+                .flag_if_supported("-Wno-ignored-qualifiers");
             for file in cpp_files {
                 cpp_build.file(dir.join(file));
             }