ANDROID: refactor build.config files to remove duplication

The build.config.* files largely contain duplicate information by their
nature. Reorganize them reduce duplication and to allow adding new
configurations without copying the definitions again.

Bug: 140224784
Change-Id: I6a3810a125b0ed48591690ca33bb5c02be58218a
Signed-off-by: Matthias Maennich <maennich@google.com>
(cherry picked from commit 7d642373db4c6c1c6ed8af02492047896beb4a47)
diff --git a/build.config.cuttlefish.x86_64 b/build.config.cuttlefish.x86_64
index 7a79036..fed773c 100644
--- a/build.config.cuttlefish.x86_64
+++ b/build.config.cuttlefish.x86_64
@@ -1,16 +1,5 @@
-ARCH=x86_64
-BRANCH=android-4.9
-CLANG_TRIPLE=x86_64-linux-gnu-
-CROSS_COMPILE=x86_64-linux-androidkernel-
+. ${ROOT_DIR}/common/build.config.common
+. ${ROOT_DIR}/common/build.config.x86_64
+
 DEFCONFIG=x86_64_cuttlefish_defconfig
-EXTRA_CMDS=''
-KERNEL_DIR=common
 POST_DEFCONFIG_CMDS="check_defconfig"
-CLANG_PREBUILT_BIN=prebuilts-master/clang/host/linux-x86/clang-r353983c/bin
-LINUX_GCC_CROSS_COMPILE_PREBUILTS_BIN=prebuilts/gcc/linux-x86/x86/x86_64-linux-android-4.9/bin
-FILES="
-arch/x86/boot/bzImage
-vmlinux
-System.map
-"
-STOP_SHIP_TRACEPRINTK=1