lttng-tools: fix build errors and warnings for musl/uClibc-ng

lttng-tools: fix build errors and warnings for musl/uClibc-ng

Add 0001-Fix-detect-dlmopen-and-disable-corresponding-tests-i.patch to
detect if dlmopen() exists and disable parts of the build accordingly if
not. This fixes a bug when building with musl or uClibc-ng.

Add 0002-Fix-src-common-pipe.h-include-sys-types.h-for-ssize_.patch to
fix an #include bug when building with musl.

Add 0003-Fix-warning-src-bin-lttng-utils.c-cast-incompatible-.patch to
remove compilation warnings.

All three new patches are in upstream's master branch as of this date
and will be part of an eventual release.

Fixes:

  http://autobuild.buildroot.net/results/e37a5c69e2a9f9cd7c0705331e205c1ee20808e7/
  (musl)

  http://autobuild.buildroot.net/results/b2670e6d1928649aefa7fbc748858e6036585f01/
  (uclibc)

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>