Add color format_to overloads

* Fix variable size basic_memory_buffer colorization
* Fix an unused arguments warning on GCC that blocks the CI otherwise
* Ref #1842
* Ref #1593

test/gtest-extra.h

@@ -145,7 +145,13 @@ std::string read(fmt::file& f, size_t count);
               read(file, fmt::string_view(expected_content).size()))
 
 #else
-#  define EXPECT_WRITE(file, statement, expected_output) SUCCEED()
+#  define EXPECT_WRITE(file, statement, expected_output) \
+    do {                                                 \
+      (void)(file);                                      \
+      (void)(statement);                                 \
+      (void)(expected_output);                           \
+      SUCCEED();                                         \
+    } while (false)
 #endif  // FMT_USE_FCNTL
 
 template <typename Mock> struct ScopedMock : testing::StrictMock<Mock> {