ocurl: needs pkg-config and/or bc

[mseri]

When pkg-config is not instlled it sometimenps fails with

#=== ERROR while compiling ocurl.0.9.2 ========================================#
# context              2.2.0~alpha~dev | linux/x86_64 | ocaml-base-compiler.5.0.0 | file:///home/opam/opam-repository
# path                 ~/.opam/5.0/.opam-switch/build/ocurl.0.9.2
# command              ~/.opam/opam-init/hooks/sandbox.sh build ./configure
# exit-code            1
# env-file             ~/.opam/log/ocurl-7-7af241.env
# output-file          ~/.opam/log/ocurl-7-7af241.out
### output ###
# checking for gcc... gcc
# checking whether the C compiler works... yes
# checking for C compiler default output file name... a.out
# checking for suffix of executables... 
# checking whether we are cross compiling... no
# checking for suffix of object files... o
# checking whether we are using the GNU C compiler... yes
# checking whether gcc accepts -g... yes
# checking for gcc option to accept ISO C89... none needed
# checking for libcurl cflags... ./configure: line 2857: pkg-config: command not found
# 
# checking for libcurl libs... ./configure: line 2872: pkg-config: command not found
# -lcurl
# checking for libcurl version >= 7.28.0... ./configure: line 2887: pkg-config: command not found
# ./configure: line 2888: pkg-config: command not found
# /usr/bin/curl-config: 1: /usr/bin/curl-config: bc: not found
# /usr/bin/curl-config: 1: /usr/bin/curl-config: bc: not found
# /usr/bin/curl-config: 113: test: Illegal number: 
# requested version 7.28.0 is newer than existing 7.58.0
# configure: error: libcurl 7.58.0 is too old

[mseri]

This is no longer explicitly a dependency since conf-libcurl.2