-LUA_SHLIBS ?= $(shell pkg-config --silence-errors --libs lua5.1)
-LUA_LIBS ?= $(if $(LUA_SHLIBS),$(LUA_SHLIBS),$(firstword $(wildcard /usr/lib/liblua.a /usr/local/lib/liblua.a /opt/local/lib/liblua.a)))
-LUA_CFLAGS ?= $(shell pkg-config --silence-errors --cflags lua5.1)
+LUA_SHLIBS = $(shell pkg-config --silence-errors --libs lua5.1)
+LUA_LIBS = $(if $(LUA_SHLIBS),$(LUA_SHLIBS),$(firstword $(wildcard /usr/lib/liblua.a /usr/local/lib/liblua.a /opt/local/lib/liblua.a)))
+LUA_CFLAGS = $(shell pkg-config --silence-errors --cflags lua5.1)