Use managed cmark include path on Windows

Author: danjboyd

ObjcMarkdown/GNUmakefile

@@ -5,6 +5,7 @@ LIBRARY_NAME = ObjcMarkdown
 CMARK_PKG := $(shell pkg-config --exists cmark 2>/dev/null && echo cmark || echo libcmark)
 CMARK_CFLAGS := $(shell pkg-config --cflags $(CMARK_PKG) 2>/dev/null)
 CMARK_LIBS := $(shell pkg-config --libs $(CMARK_PKG) 2>/dev/null)
+CMARK_MANAGED_INCLUDE := $(shell if [ -n "$$GP_GNUSTEP_CLI_ROOT" ]; then root="$$(cygpath -u "$$GP_GNUSTEP_CLI_ROOT" 2>/dev/null)"; if [ -n "$$root" ]; then printf '%s/clang64/include' "$$root"; fi; fi)
 OBJCMARKDOWN_ENABLE_TOML_THEME ?= 1
 
 ObjcMarkdown_OBJC_FILES = OMMarkdownRenderer.m OMTheme.m OMMarkdownParsingOptions.m
@@ -14,9 +15,13 @@ ifneq (,$(findstring mingw,$(GNUSTEP_HOST_OS)))
 ObjcMarkdown_OBJCFLAGS += -include sys/types.h "-Dmode_t=unsigned short"
 ObjcMarkdown_LIBRARIES_DEPEND_UPON += -lgdiplus
 ifeq ($(strip $(CMARK_CFLAGS)),)
+ifneq ($(strip $(CMARK_MANAGED_INCLUDE)),)
+CMARK_CFLAGS := -I$(CMARK_MANAGED_INCLUDE)
+else
 CMARK_CFLAGS := -I/clang64/include
 endif
 endif
+endif
 ifeq ($(OBJCMARKDOWN_ENABLE_TOML_THEME),1)
 ObjcMarkdown_C_FILES = ../third_party/tomlc99/toml.c
 ObjcMarkdown_CPPFLAGS += -I../third_party/tomlc99