Revision 1818801

Use LZ4_versionNumber() to reduce the version requirement for LZ4

LZ4_versionNumber() was introduced in r120, which is more widely available than
1.7.3, when LZ4_versionString() was introduced.

* subversion/include/private/svn_subr_private.h
  (svn_lz4__runtime_version): Change the return type to int

* subversion/libsvn_subr/compress_lz4.c
  (svn_lz4__compiled_version): Compose the version string from the
    LZ4_VERSION_{MAJOR,MINOR,RELEASE} defines
  (svn_lz4__runtime_version): Return the integer version value

* subversion/libsvn_subr/sysinfo.c
  (svn_sysinfo__linked_libs): Decompose the version number and build the
    version string