Findursa: specify OpenSSL directory

Signed-off-by: Andrei Lebedev <lebdron@gmail.com>

cmake/Modules/Findursa.cmake

@@ -1,6 +1,9 @@
 add_library(ursa UNKNOWN IMPORTED)
 find_package(OpenSSL REQUIRED)
 
+get_filename_component(_OPENSSL_INCLUDE_PARENT_DIR ${OPENSSL_INCLUDE_DIR} DIRECTORY)
+set(OPENSSL_ROOT_DIR ${_OPENSSL_INCLUDE_PARENT_DIR})
+
 set(URL     "https://github.com/hyperledger/ursa/")
 set(VERSION "d425dc2f721659f6bdec50a91d3cb9a1d21ec3f3")
 
@@ -17,7 +20,7 @@ externalproject_add(hyperledger_ursa
   GIT_REPOSITORY    ${URL}
   GIT_TAG           ${VERSION}
   BUILD_IN_SOURCE   1
-  BUILD_COMMAND     cargo build --release --no-default-features --features="ffi"
+  BUILD_COMMAND     ${CMAKE_COMMAND} -E env OPENSSL_DIR=${OPENSSL_ROOT_DIR} cargo build --release --no-default-features --features="ffi"
   CONFIGURE_COMMAND "" # remove configure step
   UPDATE_COMMAND    "" # remove update step
   INSTALL_COMMAND   "" # remove install step