x86_64 use defconfig fragments.

This allows us to check that the configs in the
corresponding fragments are actually enabled properly.

Other architectures will be fixed in other CLs. In
case of any issues, this allows for a smaller
revert.

Test: TH
Change-Id: I1004a2ef331d0b46be73066ff6dae215f50a6bac
diff --git a/BUILD.bazel b/BUILD.bazel
index a6ceb1d..505a34a 100644
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -218,6 +218,10 @@
     arch = "x86_64",
     base_kernel = "//common:kernel_x86_64",
     build_config = "build.config.virtual_device.x86_64",
+    defconfig_fragments = [
+        "virtual_device_core.fragment",
+        "virtual_device.fragment",
+    ],
     make_goals = [
         "modules",
     ],
diff --git a/build.config.virtual_device.x86_64 b/build.config.virtual_device.x86_64
index 1cfcb08..7ced9a1 100644
--- a/build.config.virtual_device.x86_64
+++ b/build.config.virtual_device.x86_64
@@ -2,17 +2,3 @@
 
 . ${ROOT_DIR}/${KERNEL_DIR}/build.config.x86_64
 
-DEFCONFIG=vd_x86_64_gki_defconfig
-
-# HACK: bug in bash 5.2 that if the last command of the eval in a subshell is not a built-in
-#   command, the subshell exits prematurely. This is fixed in 5.2.15 but we leave
-#   this hack in until bash becomes hermetic (unlikely).
-#   See b/275468906#comment8
-PRE_DEFCONFIG_CMDS="mkdir -p \${OUT_DIR}/arch/x86/configs/ && \
-    KCONFIG_CONFIG=\${OUT_DIR}/arch/x86/configs/${DEFCONFIG} \
-        ${ROOT_DIR}/${KERNEL_DIR}/scripts/kconfig/merge_config.sh -m -r \
-        ${ROOT_DIR}/${KERNEL_DIR}/arch/x86/configs/gki_defconfig \
-        ${ROOT_DIR}/common-modules/virtual-device/virtual_device_core.fragment \
-        ${ROOT_DIR}/common-modules/virtual-device/virtual_device.fragment && \
-    true"
-POST_DEFCONFIG_CMDS=""