Don't assume that Windows is building on MSVC

The flag /utf-8 is supported by cl.exe, but gcc.exe interprets it as a
non-existent linker script.

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## 0.37 (unreleased)
 
+### Build
+
+Fixed an issue with building on Windows with gcc.
+
 ## 0.36.1 (released 17th September 2022)
 
 Fixed a release script that prevented 0.36.0 from including Windows

build.rs

@@ -107,7 +107,7 @@ impl TreeSitterParser {
         }
 
         let mut build = cc::Build::new();
-        if cfg!(windows) {
+        if cfg!(target_env = "msvc") {
             build.flag("/utf-8");
         }
         build.include(&dir).warnings(false); // ignore unused parameter warnings