gettop: fix symlink detection

Summary: We must use the -P flag for pwd to properly get $PWD from the environment *with* symlinks. Otherwise symlink
detection is broken and anything we do using $(gettop) at the top of a symlinked path won't work properly. I noticed this
issue while running on a system that has a SSD RAID symlinked to my android build home directory, which is ~/ssd_storage.
The top in this instance is a symlink, which means that gettop() returns my home path, or the path above the symlink
directory (but not the symlinked directory). This is a major issue in case developers choose to use $(gettop),
$ANDROID_BUILD_TOP, or $T (doesn't really matter either way).

Test Plan: Create a symlink and sync android source into the path. Open up the symlink, run envsetup.sh, and check
$(gettop) output.

While this isn't the best solution, it fixes an issue without creating new issues.

Change-Id: I65bc345753805e6161098d2af6e0bee0b07d37b1
Lets show what we are building with

Conflicts:
	core/dumpvar.mk
GCC Freedom (only)

.
.
This will allow you the freedom of using any custom toolchain of your choice,
provided you follow a few simple rules:

RULE #1: Both the androideabi and armeabi toolchain folders of your choice HAVE to
be named like the following:

for androideabi, the folder has to be prefixed with: arm-linux-androideabi-
and for arm-eabi, the folder has to be prefixed with: arm-eabi-

ex:

If you want to use GCC-4.8 as your toolchain of choice, both the androideabi and
armeabi folders have to look like this:

arm-linux-androideabi-4.8
arm-eabi-4.8

if you want them to be different, say, 4.8 for the arm-eabi and 4.9 for androideabi,
then they should look like this:

arm-eabi-4.8
arm-linux-androideabi-4.9

Take note, that if usining linaro, you will have to clone in the toolchain twice as
this method requires two different folders (the way it should be IMO). You would need
to rename one of the clones to arme-abi- and the other to arm-linux-androideabi-.

RULE #2: The source is configured to build with GCC 4.7 for androideabi and GCC 4.7 for
armeabi "by default" (in core/combo/TARGET_linux-arm.mk) unless you are to specify an alternate
target chain in build/core/TARGET_linux-arm.mk (lines 50 & 51). So if you want to use a different chain,
you'll need to change the chain number at the end of those two lines.

Say you wanted to use a 4.8 chain instead for armeabi and 4.9 for androideabi.. You would
just change the numbers at the end of both:

TARGET_GCC_VERSION_ARM := 4.8
TARGET_GCC_VERSION_AND := 4.9

Notice at the end of each line one is for ARM and one is for AND which hints at armeabi
and androideabi.

Remember, that this simple number change you specify at the end will decide
which toolchain you will use. So if you would rather use a 4.6 GCC, just change the
number to 4.6.

You also need to make sure rule number 1 is observed if you do this.. Can't build with
an alternate chain if one is not present ;)

RULE #3: Using higher than 4.7 GCC requires a few extra commits to source. These can be
found on my github account: https://github.com/IAmTheOneTheyCallNeo
If you have any questions or problems, feel free to message me and I will help if/when I can.
-Neo

Conflicts:
	core/tasks/kernel.mk