Update missing zstd error message in configure

Authored-by: NKaren Huddleston <khuddleston@pivotal.io>

configure

@@ -10864,7 +10864,10 @@ _ACEOF
   LIBS="-lzstd $LIBS"
 
 else
-  as_fn_error $? "zstd library not found." "$LINENO" 5
+  as_fn_error $? "zstd library not found
+If you have libzstd already installed, see config.log for details on the
+failure.  It is possible the compiler isn't looking in the proper directory.
+Use --without-zstd to disable zstd support." "$LINENO" 5
 fi
 
 fi

configure.in

@@ -1315,7 +1315,10 @@ fi
 
 if test "$with_zstd" = yes; then
   AC_CHECK_LIB(zstd, ZSTD_compressCCtx, [],
-               [AC_MSG_ERROR([zstd library not found.])])
+               [AC_MSG_ERROR([zstd library not found
+If you have libzstd already installed, see config.log for details on the
+failure.  It is possible the compiler isn't looking in the proper directory.
+Use --without-zstd to disable zstd support.])])
 fi
 
 if test "$with_quicklz" = yes; then