libzstd: Fix pkgconfig paths for cross compilation

pkgconfig needs to override these.

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

utils/zstd/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=zstd
 PKG_VERSION:=1.4.2
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://codeload.github.com/facebook/zstd/tar.gz/v$(PKG_VERSION)?
@@ -68,6 +68,12 @@ endif
 TARGET_CFLAGS += -flto
 TARGET_LDFLAGS += -Wl,--as-needed
 
+define Build/InstallDev
+	$(call Build/InstallDev/cmake,$(1))
+	$(SED) 's,/usr/include,$$$${prefix}/include,g' $(1)/usr/lib/pkgconfig/libzstd.pc
+	$(SED) 's,/usr/lib,$$$${prefix}/lib,g' $(1)/usr/lib/pkgconfig/libzstd.pc
+endef
+
 define Package/libzstd/install
 	$(INSTALL_DIR) $(1)/usr/lib
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libzstd.so* $(1)/usr/lib/