Fix issue caused by 10.14 SDK Silently killing off OpenGL functionality.

danmaku.xcodeproj/project.pbxproj

@@ -566,7 +566,7 @@
 				MTL_FAST_MATH = YES;
 				ONLY_ACTIVE_ARCH = YES;
 				OTHER_CFLAGS = "-DNCURSES_UNCTRL_H_incl";
-				SDKROOT = macosx;
+				SDKROOT = macosx10.13;
 				SYSTEM_HEADER_SEARCH_PATHS = /opt/local/include/;
 				USER_HEADER_SEARCH_PATHS = (
 					"$(PROJECT_DIR)/../game/include/expect/include",
@@ -626,7 +626,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				MTL_FAST_MATH = YES;
 				OTHER_CFLAGS = "-DNCURSES_UNCTRL_H_incl";
-				SDKROOT = macosx;
+				SDKROOT = macosx10.13;
 				SYSTEM_HEADER_SEARCH_PATHS = /opt/local/include/;
 				USER_HEADER_SEARCH_PATHS = (
 					"$(PROJECT_DIR)/../game/include/expect/include",