Test for existence of strerror.

SunOS 4.1 claims that it is __STDC__, but it does not have strerror
in string.h.  Instead of using __STDC__, this puts a direct test
for strerror in configure, and uses that information in gzguts.h.

configure

@@ -367,6 +367,21 @@ EOF
   fi
 fi
 
+echo >> configure.log
+
+cat > $test.c <<EOF
+#include <string.h>
+#include <errno.h>
+int main() { return strlen(strerror(errno)); }
+EOF
+if try $CC $CFLAGS -o $test $test.c; then
+  echo "Checking for strerror... Yes." | tee -a configure.log
+else
+  CFLAGS="${CFLAGS} -DNO_STRERROR"
+  SFLAGS="${SFLAGS} -DNO_STRERROR"
+  echo "Checking for strerror... No." | tee -a configure.log
+fi
+
 cp -p zconf.h.in zconf.h
 
 echo >> configure.log
@@ -435,7 +450,6 @@ int main()
   return 0;
 }
 EOF
-
 if try $CC -c $CFLAGS $test.c; then
   echo "Checking whether to use vs[n]printf() or s[n]printf()... using vs[n]printf()." | tee -a configure.log
 

gzguts.h

@@ -100,7 +100,7 @@
 #  include <windows.h>
 #  define zstrerror() gz_strwinerror((DWORD)GetLastError())
 #else
-#  ifdef STDC
+#  ifndef NO_STRERROR
 #    include <errno.h>
 #    define zstrerror() strerror(errno)
 #  else