Installing via Cygwin fails #1162

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
[ERROR] The compilation of conf-libev failed at "/usr/bin/sh ./build.sh".
[ERROR] The compilation of conf-libssl failed at "/usr/bin/pkg-config
        --print-errors --exists openssl".
[ERROR] The compilation of pecu failed at
        "/cygdrive/c/Users/akihisayamada/.opam/4.14.1/bin/dune build -p pecu -j
        11".

#=== ERROR while compiling pecu.0.7 ===========================================#
# context     2.0.7 | cygwin/x86_64 | ocaml-base-compiler.4.14.1 | https://opam.ocaml.org#305a94021f92bab4c94380f6b2e3e0532390ff43
# path        ~/.opam/4.14.1/.opam-switch/build/pecu.0.7
# command     ~/.opam/4.14.1/bin/dune build -p pecu -j 11
# exit-code   1
# env-file    ~/.opam/log/pecu-858-6816c2.env
# output-file ~/.opam/log/pecu-858-6816c2.out
### output ###
# [...]
# Called from Stdune__List.map in file "otherlibs/stdune/src/list.ml"
#   (inlined), line 5, characters 19-33
# Called from Dune_engine__Load_rules.Load_rules.compile_rules in file
#   "src/dune_engine/load_rules.ml", line 310, characters 6-482
# Called from Fiber__Scheduler.exec in file "vendor/fiber/src/scheduler.ml",
#   line 76, characters 8-11
#
# I must not crash.  Uncertainty is the mind-killer. Exceptions are the
# little-death that brings total obliteration.  I will fully express my cases.
# Execution will pass over me and through me.  And when it has gone past, I
# will unwind the stack along its path.  Where the cases are handled there will
# be nothing.  Only I will remain.


#=== ERROR while compiling conf-libssl.4 ======================================#
# context     2.0.7 | cygwin/x86_64 | ocaml-base-compiler.4.14.1 | https://opam.ocaml.org#305a94021f92bab4c94380f6b2e3e0532390ff43
# path        ~/.opam/4.14.1/.opam-switch/build/conf-libssl.4
# command     /usr/bin/pkg-config --print-errors --exists openssl
# exit-code   1
# env-file    ~/.opam/log/conf-libssl-858-abfa5b.env
# output-file ~/.opam/log/conf-libssl-858-abfa5b.out
### output ###
# Package openssl was not found in the pkg-config search path.
# Perhaps you should add the directory containing `openssl.pc'
# to the PKG_CONFIG_PATH environment variable
# Package 'openssl' not found


#=== ERROR while compiling conf-libev.4-12 ====================================#
# context     2.0.7 | cygwin/x86_64 | ocaml-base-compiler.4.14.1 | https://opam.ocaml.org#305a94021f92bab4c94380f6b2e3e0532390ff43
# path        ~/.opam/4.14.1/.opam-switch/build/conf-libev.4-12
# command     /usr/bin/sh ./build.sh
# exit-code   1
# env-file    ~/.opam/log/conf-libev-858-e01822.env
# output-file ~/.opam/log/conf-libev-858-e01822.out
### output ###
# testing for libev: ............................. unavailable
#
#       The following recquired C libraries are missing: libev.
# Please install them and retry. If they are installed in a non-standard location, set the environment variables C_INCLUDE_PATH and LIBRARY_PATH accordingly and retry.
#
# For example, if they are installed in /opt/local, you can type:
#
# export C_INCLUDE_PATH=/opt/local/include
# export LIBRARY_PATH=/opt/local/lib
#
# To compile without libev support, use ./configure --disable-libev ...



<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
+- The following actions failed
| - build conf-libev  4-12
| - build conf-libssl 4
| - build pecu        0.7
+-
- No changes have been performed