Tweak libuv makefiles so they pick up custom CFLAGS

Author: brson

src/rt/libuv/config-mingw.mk

@@ -24,7 +24,7 @@ CC ?= $(PREFIX)gcc
 AR ?= $(PREFIX)ar
 E=.exe
 
-CFLAGS=$(CPPFLAGS) -g --std=gnu89 -D_WIN32_WINNT=0x0501 -Isrc/ares/config_win32
+CFLAGS+=$(CPPFLAGS) -g --std=gnu89 -D_WIN32_WINNT=0x0501 -Isrc/ares/config_win32
 LINKFLAGS=-lm
 
 CARES_OBJS += src/ares/windows_port.o

src/rt/libuv/config-unix.mk

@@ -22,7 +22,7 @@ CC ?= $(PREFIX)gcc
 AR ?= $(PREFIX)ar
 E=
 CSTDFLAG=--std=c89 -pedantic
-CFLAGS=-g
+CFLAGS+=-g
 CPPFLAGS += -Isrc/ev
 LINKFLAGS=-lm