BSD support

Makefile

@@ -4,7 +4,7 @@
 # Clean:   make clean
 # Install: make install PREFIX=/usr/local
 
-CC      ?= gcc
+CC      ?= cc
 CFLAGS  ?= -O2 -s -std=c11 -Wall -Wextra
 CPPFLAGS += -D_POSIX_C_SOURCE=200809L -D_DEFAULT_SOURCE
 LDFLAGS ?=
@@ -12,7 +12,7 @@ LDLIBS  += -lpthread
 # The matcher uses POSIX memmem(), which glibc accelerates with SIMD on
 # whatever CPU you run on. -mavx2 is harmless but unnecessary; drop it for
 # maximum portability (e.g. make MARCH="").
-MARCH   ?= -mavx2
+MARCH   ?=
 
 BINARY  := gg
 SRC     := gg.c