fix: skip building liblsof when --disable-liblsof is given

[kurok]

Summary

• Stop compiling liblsof.la when --disable-liblsof is passed to ./configure
• Guard the LTbasic2 test (which links against liblsof.la) behind the same conditional

Problem

With --disable-liblsof, the library was still compiled as noinst_LTLIBRARIES — just not installed. Since the lsof binary compiles all the library sources directly (lsof_SOURCES += ... rather than lsof_LDADD = liblsof.la), this was unnecessary work.

Approach

Rename liblsof_la_SOURCES to a plain LIBLSOF_SOURCES variable (no automake target magic). Both lsof_SOURCES and liblsof_la_SOURCES reference this shared list. The liblsof.la library target, its _CPPFLAGS, and the LTbasic2 test are now only defined inside if INSTALL_LIBLSOF.

Before (--disable-liblsof):

noinst_LTLIBRARIES = liblsof.la   # compiled but not installed

After (--disable-liblsof):

# liblsof.la is not defined at all — not compiled, not installed

Test plan

• ./configure --disable-liblsof && make builds lsof without compiling liblsof.la
• ./configure && make builds both lsof and liblsof.la (default behavior preserved)
• make check with --disable-liblsof skips LTbasic2 and passes remaining tests
• make check with default config runs LTbasic2 and passes

Closes #324