Don't assume make is gmake

*** 16,55 ****
  DIRS=$(wildcard */)
  SRCS=$(wildcard *.c)
  OBJS=$(SRCS:.c=.o)
  
  all: bin
!         make -C tests
  
  include s2n.mk
  
  libs:
!         make -C utils
!         make -C error
!         make -C stuffer
!         make -C crypto
!         make -C tls
!         make -C lib
  
  bin: libs
!         make -C bin
  
  indent:
!         make -C tests indentsource
!         make -C stuffer indentsource
!         make -C crypto indentsource
!         make -C utils indentsource
!         make -C error indentsource
!         make -C tls indentsource
!         make -C bin indentsource
  
  pre_commit_check: all indent clean
  
  clean:
!         make -C tests clean
!         make -C stuffer decruft
!         make -C crypto decruft
!         make -C utils decruft
!         make -C error decruft
!         make -C tls decruft
!         make -C bin decruft
!         make -C lib decruft
--- 16,55 ----
  DIRS=$(wildcard */)
  SRCS=$(wildcard *.c)
  OBJS=$(SRCS:.c=.o)
  
  all: bin
!         $(MAKE) -C tests
  
  include s2n.mk
  
  libs:
!         $(MAKE) -C utils
!         $(MAKE) -C error
!         $(MAKE) -C stuffer
!         $(MAKE) -C crypto
!         $(MAKE) -C tls
!         $(MAKE) -C lib
  
  bin: libs
!         $(MAKE) -C bin
  
  indent:
!         $(MAKE) -C tests indentsource
!         $(MAKE) -C stuffer indentsource
!         $(MAKE) -C crypto indentsource
!         $(MAKE) -C utils indentsource
!         $(MAKE) -C error indentsource
!         $(MAKE) -C tls indentsource
!         $(MAKE) -C bin indentsource
  
  pre_commit_check: all indent clean
  
  clean:
!         $(MAKE) -C tests clean
!         $(MAKE) -C stuffer decruft
!         $(MAKE) -C crypto decruft
!         $(MAKE) -C utils decruft
!         $(MAKE) -C error decruft
!         $(MAKE) -C tls decruft
!         $(MAKE) -C bin decruft
!         $(MAKE) -C lib decruft