kpatch-gcc: properly quote arguments

Fixes an error when the following is an argument to gcc:

'-DIPATH_IDSTR="QLogic' kernel.org 'driver"'

gcc: error: kernel.org: No such file or directory
gcc: error: driver": No such file or directory
kpatch-build: add more ancestors for vmlinux

There are a few more valid ancestors for vmlinux other than built-in.o.
This fixes errors similar to the following:

    ERROR: invalid ancestor arch/x86/lib/lib.a for arch/x86/lib/usercopy_64.o
kpatch-build: deep find performance improvement

If we have to do a deep find (e.g. search the entire tree) to find a
parent object, first try searching in the last successful deep find
directory.  This is a performance improvement in the case of a full tree
rebuild, because deep finds are very expensive, and it's not uncommon
for there to be multiple objects in a directory being linked into an
object in another directory.
kpatch-gcc: skip vdso files

vdso files aren't kpatch-compatible, and give errors like the following:

    ERROR: invalid ancestor arch/x86/vdso/vdso32-sysenter.so.dbg for arch/x86/vdso/vdso32/sysenter.o
kpatch-build: allow two parents unless the object changes

With some obscure drivers, the same object file can be linked into
multiple parent objects.  Only call this out as an error if the object
has changed, otherwise it doesn't matter.

Fixes the following issue:

    ERROR: two parent matches for drivers/media/radio/si470x/radio-si470x-common.o.
process special sections after checking for changes

There's no need to process special sections if we're returning due to no
functions changing.

Also this means we don't have to deal with extra-special usage of the
.fixup section (here's looking at you arch/x86/lib/copy_user_64.S -- we
can't patch functions in .S files anyway).
new .fixup group size algorithm

The fixup_group_size() function assumes that all .fixup rela groups end
with a jmpq instruction.  That assumption turns out to be false when you
take into account the ____kvm_handle_fault_on_reboot() macro which is
used by kvm.

This is a new, more reliable method.  It turns out that each .fixup
group is referenced by the __ex_table section.  The new algorithm goes
through the __ex_table relas to figure out the size of each .fixup
group.

Also the .fixup section is now processed before __ex_table, because it
needs to access the original __ex_table relas before the unused ones
have been stripped.

Fixes the following error:

  ERROR: vmx.o: fixup_group_size: 1554: can't find jump instruction in .fixup section
test: add slow test for rebuilding entire tree

Only gets run with the slow integration tests, not "make quick".
code review fixes
Merge pull request #428 from jpoimboe/full-tree-recompile

full tree recompilation support