Suppress a bogus warning in MSVC (#4023)

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

include/fmt/std.h

@@ -35,9 +35,11 @@
 #    if FMT_HAS_INCLUDE(<optional>)
 #      include <optional>
 #    endif
-#    if FMT_HAS_INCLUDE(<source_location>)
-#      include <source_location>
-#    endif
+#  endif
+// Use > instead of >= in the version check because <source_location> may be
+// available after C++17 but before C++20 is marked as implemented.
+#  if FMT_CPLUSPLUS > 201703L && FMT_HAS_INCLUDE(<source_location>)
+#    include <source_location>
 #  endif
 #  if FMT_CPLUSPLUS > 202002L && FMT_HAS_INCLUDE(<expected>)
 #    include <expected>

test/ranges-test.cc

@@ -17,7 +17,7 @@
 #include <utility>
 #include <vector>
 
-#if FMT_HAS_INCLUDE(<ranges>)
+#if FMT_CPLUSPLUS > 201703L && FMT_HAS_INCLUDE(<ranges>)
 #  include <ranges>
 #endif