libfmt: Fix pkgconfig paths

pkgconfig needs to override these.

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

libs/libfmt/Makefile

@@ -43,6 +43,12 @@ define Package/libfmt/description
   It can be used as a safe alternative to printf or as a fast alternative to IOStreams.
 endef
 
+define Build/InstallDev
+	$(call Build/InstallDev/cmake,$(1))
+	$(SED) 's,/usr/include,$$$${prefix}/include,g' $(1)/usr/lib/pkgconfig/fmt.pc
+	$(SED) 's,/usr/lib,$$$${exec_prefix}/lib,g' $(1)/usr/lib/pkgconfig/fmt.pc
+endef
+
 define Package/libfmt/install
 	$(INSTALL_DIR) $(1)/usr/lib
 	$(CP) $(PKG_INSTALL_DIR)/usr/lib/libfmt.so* $(1)/usr/lib/