expat: fix compilation with doc2man

Even though doc2man is explicitly disabled, it is only for the target.
Split out the options to a separate variable.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/expat/Makefile

@@ -36,7 +36,7 @@ define Package/libexpat/description
  A fast, non-validating, stream-oriented XML parsing library.
 endef
 
-CMAKE_OPTIONS += \
+OPTIONS += \
 	-DDOCBOOK_TO_MAN=OFF \
 	-DEXPAT_BUILD_TOOLS=OFF \
 	-DEXPAT_BUILD_EXAMPLES=OFF \
@@ -48,6 +48,9 @@ CMAKE_OPTIONS += \
 	-DEXPAT_NS=OFF \
 	-DEXPAT_DEV_URANDOM=OFF
 
+CMAKE_OPTIONS += $(OPTIONS)
+CMAKE_HOST_OPTIONS += $(OPTIONS)
+
 define Package/libexpat/install
 	$(INSTALL_DIR) $(1)/usr/lib
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libexpat.so.* $(1)/usr/lib/