Mostly implemented crypt-tune-costs.

Known bugs in the handling of logarithmic cost will be addressed later.
This patch will probably get shuffled to the end of the branch.

.gitignore

@@ -47,6 +47,7 @@
 /crypt.h
 /crypt-hashes.h
 /crypt-symbol-vers.h
+/crypt-tune-costs
 /libcrypt.map
 /gen-des-tables
 /test-alg-des

Makefile.am

@@ -48,6 +48,9 @@ libcrypt_la_SOURCES = \
 
 EXTRA_DIST += alg-yescrypt-platform.c
 
+sbin_PROGRAMS = crypt-tune-costs
+crypt_tune_costs_LDADD = libcrypt.la -lm
+
 pkgconfig_DATA = libxcrypt.pc
 # Install libcrypt.pc symlink to libxcrypt.pc file.
 phony_targets = \

crypt-port.h

@@ -49,6 +49,19 @@
 # define __GNUC_PREREQ__(ma, mi) __GNUC_PREREQ(ma, mi)
 #endif
 
+/* C2011 added a keyword _Noreturn with the same effect as
+   gcc's longstanding __attribute__ ((noreturn)) extension,
+   except that it is required to appear _before_ the function
+   type specifier (which must be 'void').  */
+#if (defined __STDC_VERSION__ ? __STDC_VERSION__ : 0) >= 201112 || \
+    defined _Noreturn
+# define NORETURN _Noreturn void
+#elif defined __GNUC__ && __GNUC__ >= 3
+# define NORETURN void __attribute__ ((noreturn))
+#else
+# define NORETURN void
+#endif
+
 /* While actually compiling the library, suppress the __nonnull tags
    on the functions in crypt.h, so that internal checks for NULL are
    not deleted by the compiler.  */