Undefined references to 'crypto_scalarmult' & 'crypto_scalarmult_base' - default example build

[prembo]

When building the example code according to instructions in the README the following errors result:

<snip>/xtensa-esp32-elf/bin/ld: esp-idf/libssh/liblibssh.a(curve25519.c.obj):(.literal.ssh_curve25519_build_k+0x0): undefined reference to `crypto_scalarmult'
<snip>/xtensa-esp32-elf/bin/ld: esp-idf/libssh/liblibssh.a(curve25519.c.obj):(.literal.ssh_curve25519_init+0x8): undefined reference to `crypto_scalarmult_base'
<snip>/xtensa-esp32-elf/bin/ld: esp-idf/libssh/liblibssh.a(curve25519.c.obj): in function `ssh_curve25519_build_k':
<srcbase>/esp-idf-libssh/components/libssh/libssh/src/curve25519.c:252: undefined reference to `crypto_scalarmult'
<snip>/xtensa-esp32-elf/bin/ld: <srcbase>/esp-idf-libssh/components/libssh/libssh/src/curve25519.c:255: undefined reference to `crypto_scalarmult'
<snip>/xtensa-esp32-elf/bin/ld: esp-idf/libssh/liblibssh.a(curve25519.c.obj): in function `ssh_curve25519_init':
<srcbase>/esp-idf-libssh/components/libssh/libssh/src/curve25519.c:133: undefined reference to `crypto_scalarmult_base'
<snip>/xtensa-esp32-elf/bin/ld: <srcbase>/esp-idf-libssh/components/libssh/libssh/src/curve25519.c:136: undefined reference to `crypto_scalarmult_base'

This was in addition to a couple of type cast warnings. The default settings defined in components/libssh/compat/config.h were used.

[prembo]

Problem is solved by adding ${SRC}/external/curve25519_ref.c to components/libssh/CMakeLists.txt