[XCConfig] Only include -ObjC flag when linking against a static lib

lib/cocoapods/generator/xcconfig/aggregate_xcconfig.rb

@@ -49,8 +49,10 @@ module Pod
         # @return [Xcodeproj::Config]
         #
         def generate
+          includes_static_libs = !target.requires_frameworks?
+          includes_static_libs ||= target.pod_targets.flat_map(&:file_accessors).any? { |fa| !fa.vendored_libraries.empty? }
           config = {
-            'OTHER_LDFLAGS' => '$(inherited) ' + XCConfigHelper.default_ld_flags(target),
+            'OTHER_LDFLAGS' => '$(inherited) ' + XCConfigHelper.default_ld_flags(target, includes_static_libs),
             'PODS_ROOT' => target.relative_pods_root,
             'GCC_PREPROCESSOR_DEFINITIONS' => '$(inherited) COCOAPODS=1',
           }

lib/cocoapods/generator/xcconfig/xcconfig_helper.rb

@@ -31,8 +31,9 @@ module Pod
         #         while `-fobjc-arc` is included only if requested in the
         #         Podfile.
         #
-        def self.default_ld_flags(target)
-          ld_flags = '-ObjC'
+        def self.default_ld_flags(target, includes_static_libraries = false)
+          ld_flags = ''
+          ld_flags << '-ObjC' if includes_static_libraries
           if target.podfile.set_arc_compatibility_flag? &&
               target.spec_consumers.any?(&:requires_arc?)
             ld_flags << ' -fobjc-arc'