configs/pc_x86_64_{bios, efi}_defconfig: add midding libelf kernel dependency

objtool built by the kernel requires libelf

ldd output/build/linux-6.1.24/tools/objtool/objtool
  linux-vdso.so.1
  libelf.so.1 => output/host/lib/libelf.so.1

While updating the kernel [1] we forgot to select
BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF to provide Buildroot's host-libelf.
Using host-libelf avoid linking with libelf installed on the host or
failing to build objtool if libelf is not installed.

[1] d45538f2e7acc1b330b191d559a81e8c1a961648

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/4889436869
https://gitlab.com/buildroot.org/buildroot/-/jobs/4889436872

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/pc_x86_64_bios_defconfig

@@ -32,6 +32,7 @@ BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/pc/linux.config"
 BR2_LINUX_KERNEL_INSTALL_TARGET=y
 BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
+BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF=y
 
 # Firmware
 BR2_PACKAGE_LINUX_FIRMWARE=y

configs/pc_x86_64_efi_defconfig

@@ -33,6 +33,7 @@ BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/pc/linux.config"
 BR2_LINUX_KERNEL_INSTALL_TARGET=y
 BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y
+BR2_LINUX_KERNEL_NEEDS_HOST_LIBELF=y
 
 # Firmware
 BR2_PACKAGE_LINUX_FIRMWARE=y