Change macros for autotools

[rzerres]

Summary of changes

This pull request includes following changes or fixes.

• Substitute depreciated macro AC_TRY_COMPILE
• Substitute obsolete macro AC_PROG_CC_C99
• Replace the obsoleted AC_PROG_LIBTOOL with LT_INIT

Description

Using Arch Linux (Universal time: Mo 2021-05-10 11:11:07 UTC), that offers lastest toolchain for autotools, the given master branch renders with errors.
I adapted the relevant macros in configure.ac to meet best practice. This fixes the compile issues.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have confirmed my fix is effective or that my feature works

[piste-jp]

As you see, the PR would break the build of the first target, RHEL7 x86_64. Because the build check on CentOS7 was failed.

At this time, I can't drop RHEL7/CentOS7 from the list. Please provide a complete fix to work on all distributions on the checker.

https://github.com/LinearTapeFileSystem/ltfs/blob/master/.github/CONTRIBUTING.md

[piste-jp]

As I commented, please provide a fix to work on all existing checkers.

[piste-jp]

Thanks!

It looks great to me.