kernel: Fix vdso32 building for 4.19+ kernels

This flag has been renamed in 4.19 kernels
https://android.googlesource.com/kernel/common/+/refs/heads/android-4.19-stable/arch/arm64/kernel/vdso32/Makefile#13

Change-Id: I92db29aa124da7c9fc63454d9443373bdc2e16e7

config/BoardConfigKernel.mk

@@ -95,6 +95,7 @@ endif
 # Needed for CONFIG_COMPAT_VDSO, safe to set for all arm64 builds
 ifeq ($(KERNEL_ARCH),arm64)
    KERNEL_CROSS_COMPILE += CROSS_COMPILE_ARM32="$(KERNEL_TOOLCHAIN_arm)/$(KERNEL_TOOLCHAIN_PREFIX_arm)"
+   KERNEL_CROSS_COMPILE += CROSS_COMPILE_COMPAT="$(KERNEL_TOOLCHAIN_arm)/$(KERNEL_TOOLCHAIN_PREFIX_arm)"
 endif
 
 # Clear this first to prevent accidental poisoning from env