Our need for "make external" was plagued with problems. First and formost,
it was annoying - people need to be told to run "make all external" instead
of just "make". And as a Vlad recently discovered, it strangely relied on a
debug-mode build to have happened, and also "make clean" doesn't undo what
"make external" did.

"make external" had a glorious past, but today all that was left of it
is 3 measly tests which we compile from external/glibc-testsuite: malloc,
getcwd and clock. These tiny tests - 3 out of 796 tests (!!) in the full
glibc test suite - aren't really important enough to cause all this
"make external" mess. So this patch removes them, and the need for a
"make external".

If we'll ever want to bring back these tests, I think we need to delete the
partial external/glibc-testsuite directory, and bring the *full* glibc
test suite of 796 tests, into a separate module. The glibc test suite can be
downloaded together with the glibc source code - they are all files named
tst-*.c in the glibc source tree.

Signed-off-by: Nadav Har'El <nyh@cloudius-systems.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>