kernel: Link against prebuilt openssl

Using preinstalled system headers and libraries is no longer allowed.
So we're gonna make our own prebuilts/openssl so we can build kernels.

Change-Id: Ic5bc3b14c37b3bca352932c6f19a592377dbaf27

config/BoardConfigKernel.mk

@@ -110,6 +110,11 @@ endif
 ifeq ($(HOST_OS),darwin)
   KERNEL_MAKE_FLAGS += C_INCLUDE_PATH=$(BUILD_TOP)/external/elfutils/libelf:/usr/local/opt/openssl/include
   KERNEL_MAKE_FLAGS += LIBRARY_PATH=/usr/local/opt/openssl/lib
+else
+  KERNEL_MAKE_FLAGS += C_INCLUDE_PATH=$(BUILD_TOP)/prebuilts/openssl/$(HOST_OS)-x86/1.1.1/include
+  KERNEL_MAKE_FLAGS += LIBRARY_PATH=$(BUILD_TOP)/prebuilts/openssl/$(HOST_OS)-x86/1.1.1/lib/x86_64-linux-gnu
+  KERNEL_MAKE_FLAGS += HOSTCFLAGS="-L $(BUILD_TOP)/prebuilts/openssl/$(HOST_OS)-x86/1.1.1/lib/x86_64-linux-gnu"
+  KERNEL_MAKE_FLAGS += HOSTLDFLAGS="-L $(BUILD_TOP)/prebuilts/openssl/$(HOST_OS)-x86/1.1.1/lib/x86_64-linux-gnu"
 endif
 
 ifneq ($(TARGET_KERNEL_ADDITIONAL_FLAGS),)