Add a 2 width option of clang format.

Make the default the 4 tab space version.

Add a link to the 2 space version for libbacktrace.

The only other difference between the 4 space and 2 space tab version
is that the 2 space tab version allows short functions on a single line.
This is for things like constructors, short destructors, or accessor
functions. I believe this is closer to the Google C++ style guide.

Bug: 36046320

Test: NA
Change-Id: Ida08db18902eeb101f42869dd5590182529d54ef

.clang-format

-BasedOnStyle: Google
-AllowShortBlocksOnASingleLine: false
-AllowShortFunctionsOnASingleLine: false
-
-AccessModifierOffset: -2
-ColumnLimit: 100
-CommentPragmas: NOLINT:.*
-DerivePointerAlignment: false
-IndentWidth: 4
-PointerAlignment: Left
-TabWidth: 4
-UseTab: Never
-PenaltyExcessCharacter: 32

.clang-format

+.clang-format-4
\ No newline at end of file

.clang-format-2

+BasedOnStyle: Google
+AllowShortBlocksOnASingleLine: false
+AllowShortFunctionsOnASingleLine: true
+
+AccessModifierOffset: -1
+ColumnLimit: 100
+CommentPragmas: NOLINT:.*
+DerivePointerAlignment: false
+IndentWidth: 2
+PointerAlignment: Left
+TabWidth: 2
+UseTab: Never
+PenaltyExcessCharacter: 32

.clang-format-4

+BasedOnStyle: Google
+AllowShortBlocksOnASingleLine: false
+AllowShortFunctionsOnASingleLine: false
+
+AccessModifierOffset: -2
+ColumnLimit: 100
+CommentPragmas: NOLINT:.*
+DerivePointerAlignment: false
+IndentWidth: 4
+PointerAlignment: Left
+TabWidth: 4
+UseTab: Never
+PenaltyExcessCharacter: 32

libbacktrace/.clang-format

+../.clang-format-2
\ No newline at end of file