Release 2.12.7.4

These changes are per calc version 2.12.7.3:

Requiring calc shell scripts to use -s -f at the end of the
initial #! line.

Fixed /tmp/mersenne example in calc(1) man page.

Added make variable ${ARCH_CFLAGS}.  The ${ARCH_CFLAGS} is
added after ${CCMISC} and before ${EXTRA_CFLAGS} when building
the ${CFLAGS} for compiling C code.  are ${CC} when compiling
C files.  The default value is:

ARCH_CFLAGS= -march=native

which directs C compiler to compile for the native machine.
To disable use of '-march=native', set ARCH_CFLAGS to the empty
string as in:

make all ARCH_CFLAGS=

To make calc RPMs more portable, they are compiled with an
empty ARCH_CFLAGS.

These changes are per calc version 2.12.7.4:

Fixed issues relating to compiling on macOS.  Fixed issues
where <unistd.h> is needed.

have_memmv.c

@@ -1,7 +1,7 @@
 /*
  * have_memmv - Determine if we have memmove()
  *
- * Copyright (C) 1999  Landon Curt Noll
+ * Copyright (C) 1999,2021  Landon Curt Noll
  *
  * Calc is open software; you can redistribute it and/or modify it under
  * the terms of the version 2.1 of the GNU Lesser General Public License
@@ -40,6 +40,7 @@
 
 
 #include <stdio.h>
+#include <string.h>
 
 #define MOVELEN 3