Fix regression of yhirose#2121 (yhirose#2126)

Author: DarthGandalf

cmake/httplibConfig.cmake.in

@@ -39,7 +39,25 @@ if(@HTTPLIB_IS_USING_BROTLI@)
 endif()
 
 if(@HTTPLIB_IS_USING_ZSTD@)
-	find_dependency(zstd)
+	set(httplib_fd_zstd_quiet_arg)
+	if(${CMAKE_FIND_PACKAGE_NAME}_FIND_QUIETLY)
+		set(httplib_fd_zstd_quiet_arg QUIET)
+	endif()
+	set(httplib_fd_zstd_required_arg)
+	if(${CMAKE_FIND_PACKAGE_NAME}_FIND_REQUIRED)
+		set(httplib_fd_zstd_required_arg REQUIRED)
+	endif()
+	find_package(zstd QUIET)
+	if(NOT zstd_FOUND)
+		find_package(PkgConfig ${httplib_fd_zstd_quiet_arg} ${httplib_fd_zstd_required_arg})
+		if(PKG_CONFIG_FOUND)
+			pkg_check_modules(zstd ${httplib_fd_zstd_quiet_arg} ${httplib_fd_zstd_required_arg} IMPORTED_TARGET libzstd)
+
+			if(TARGET PkgConfig::zstd)
+				add_library(zstd::libzstd ALIAS PkgConfig::zstd)
+			endif()
+		endif()
+	endif()
 	set(httplib_zstd_FOUND ${zstd_FOUND})
 endif()