Inline crt-static choice for pc-windows-msvc

This avoids the possibility of a duplicate or conflicting crt-static
command line option sent to rustc.

src/bootstrap/lib.rs

@@ -658,8 +658,12 @@ impl Build {
 
     /// Returns if this target should statically link the C runtime, if specified
     fn crt_static(&self, target: Interned<String>) -> Option<bool> {
-        self.config.target_config.get(&target)
-            .and_then(|t| t.crt_static)
+        if target.contains("pc-windows-msvc") {
+            Some(true)
+        } else {
+            self.config.target_config.get(&target)
+                .and_then(|t| t.crt_static)
+        }
     }
 
     /// Returns the "musl root" for this `target`, if defined