Use gnu -o flag for obj out path instead of -Fo when using gcc & g++ …

…on Windows (#820)

src/lib.rs

@@ -522,12 +522,14 @@ impl Build {
         let mut cmd = compiler.to_command();
         let is_arm = target.contains("aarch64") || target.contains("arm");
         let clang = compiler.family == ToolFamily::Clang;
+        let gnu = compiler.family == ToolFamily::Gnu;
         command_add_output_file(
             &mut cmd,
             &obj,
             self.cuda,
             target.contains("msvc"),
             clang,
+            gnu,
             false,
             is_arm,
         );
@@ -1377,6 +1379,7 @@ impl Build {
         let msvc = target.contains("msvc");
         let compiler = self.try_get_compiler()?;
         let clang = compiler.family == ToolFamily::Clang;
+        let gnu = compiler.family == ToolFamily::Gnu;
 
         let (mut cmd, name) = if msvc && asm_ext == Some(AsmFileExt::DotAsm) {
             self.msvc_macro_assembler()?
@@ -1396,7 +1399,9 @@ impl Build {
             )
         };
         let is_arm = target.contains("aarch64") || target.contains("arm");
-        command_add_output_file(&mut cmd, &obj.dst, self.cuda, msvc, clang, is_asm, is_arm);
+        command_add_output_file(
+            &mut cmd, &obj.dst, self.cuda, msvc, clang, gnu, is_asm, is_arm,
+        );
         // armasm and armasm64 don't requrie -c option
         if !msvc || !is_asm || !is_arm {
             cmd.arg("-c");
@@ -3578,10 +3583,11 @@ fn command_add_output_file(
     cuda: bool,
     msvc: bool,
     clang: bool,
+    gnu: bool,
     is_asm: bool,
     is_arm: bool,
 ) {
-    if msvc && !clang && !cuda && !(is_asm && is_arm) {
+    if msvc && !clang && !gnu && !cuda && !(is_asm && is_arm) {
         let mut s = OsString::from("-Fo");
         s.push(&dst);
         cmd.arg(s);