package/qemu: disable curl for the host variant

package/qemu: disable curl for the host variant

Under certain circumstances (host distribution, openssl version),
the qemu-system binary fail to start:

qemu-system-aarch64: symbol lookup error: /lib64/libssh.so.4: undefined symbol: EVP_KDF_ctrl, version OPENSSL_1_1_1b

There is no problem when only host-qemu is built, but it's linked with /lib64/libcurl.so.4
$ make host-qemu
$ ldd output/host/bin/qemu-system-aarch64
        [...]
	libcurl.so.4 => /lib64/libcurl.so.4 (0x00007fb21cb57000)
	libssh.so.4 => /lib64/libssh.so.4 (0x00007fb21c35d000)
	libpsl.so.5 => /lib64/libpsl.so.5 (0x00007fb21c34a000)
	libssl.so.1.1 => /lib64/libssl.so.1.1 (0x00007fb21c2b4000)

Note: /lib64/libcurl.so.4 is linked with libssh and libssl:
$ ldd /lib64/libcurl.so.4
	[...]
	libssh.so.4 => /lib64/libssh.so.4 (0x00007f90d8efd000)
	libpsl.so.5 => /lib64/libpsl.so.5 (0x00007f90d8eea000)
	libssl.so.1.1 => /lib64/libssl.so.1.1 (0x00007f90d8e54000)

Continue the build.
$ make

We can notice that qemu_aarch64_virt_defconfig set
BR2_LINUX_KERNEL_NEEDS_HOST_OPENSSL=y

So host-openssl package is built and this is the problem:

$ ldd output/host/bin/qemu-system-aarch64
	[...]
	libcurl.so.4 => /lib64/libcurl.so.4 (0x00007f3adb444000)
	libssh.so.4 => /lib64/libssh.so.4 (0x00007f3adac4a000)
	libpsl.so.5 => /lib64/libpsl.so.5 (0x00007f3adac37000)
	libssl.so.1.1 => /home/naourr/buildroot/test/qemu_aarch64_virt_defconfig-master/host/lib/libssl.so.1.1 (0x00007f3adaba8000)

qemu-system-aarch64: symbol lookup error: /lib64/libssh.so.4: undefined symbol: EVP_KDF_ctrl, version OPENSSL_1_1_1b

This is due to the build system trying to find libcurl using
pkg-config or curl-config.

libcurl is used by the QEMU Block driver for CURL images and
elf2dmp tool which is not needed.
Instead of adding host-libcurl dependency, we can disable it
entierely.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>