When autoconf was checking for libuv features, the LIBUV_CFLAGS was not added to CFLAGS and LIBUV_LIBS to LIBS which resulted in false negatives.
Use AX_SAVE_FLAGS and AX_RESTORE_FLAGS to temporarily add LIBUV_CFLAGS and LIBUV_LIBS to their respective variables.
(cherry picked from commit f063ee27)
Closes #3366 (closed)