vanir_config v1.0.1: introduce a centralized location for custom build flags

The prime directive of this config is to provide a simple centralized
interface to allow different custom build improvements and configurations
with respect to their set status in device trees.

Revisions should respect both Clang and GCC compilers for compatibility.

current build configurations:
BONE_STOCK := set true to override all vanir_config variables
NO_DEBUG_SYMBOL_FLAGS := true removes debugging code insertions from assert.h macros and GDB
MAXIMUM_OVERDRIVE := true disables address sanitizer, set in $(BUILD_SYSTEM)/core/clang/config.mk
USE_GRAPHITE := true adds graphite cflags to turn on graphite
USE_FSTRICT_FLAGS := true builds with fstrict-aliasing (thumb and arm)
FSTRICT_ALIASING_WARNING_LEVEL := 0-3 for what is considered an aliasing violation

PS2: import only in config.mk and give values set in device trees priority
PS3: whitespace
PS9: Hope this helps.
PS12: Ensure that clang flags (set before the clang target makefiles would stomp on them) are set
      Set same clang flags for arm64
PS14: use cflag precedence to handle default thumb -fno-strict-aliasing
PS15: arm and thumb cflags have -fomit-frame-pointer already
      remove newline before fstrict flags so TARGET_linux-arm cflags don't cause ccache misses if no optional flags are set
PS16: force proper ordering of -g0 in more cases
      don't double-tap DNDEBUG all over the place

Change-Id: I988f097befbf2fd19672b8eb98bbb012deccad42