From: Jo-Philipp Wich <jo@mein.io>
Date: Wed, 11 Jan 2017 03:36:04 +0100
Subject: [PATCH] cmcurl: link librt

When cmake is linked against LibreSSL, there might be an indirect
dependency on librt on certain systems if LibreSSL's libcrypto uses
clock_gettime() from librt:

    [ 28%] Linking C executable LIBCURL
    .../lib/libcrypto.a(getentropy_linux.o): In function `getentropy_fallback':
    getentropy_linux.c:(.text+0x16d): undefined reference to `clock_gettime'
    getentropy_linux.c:(.text+0x412): undefined reference to `clock_gettime'
    collect2: error: ld returned 1 exit status
    make[5]: *** [Utilities/cmcurl/LIBCURL] Error 1

Modify the cmcurl CMakeLists.txt to check for clock_gettime() in librt
and unconditionally link the rt library when the symbol is found.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
---
--- a/Utilities/cmcurl/CMakeLists.txt
+++ b/Utilities/cmcurl/CMakeLists.txt
@@ -648,6 +648,14 @@ if(CURL_USE_OPENSSL)
   endif()
   set(SSL_ENABLED ON)
   set(USE_OPENSSL ON)
+  check_library_exists("rt" clock_gettime "" HAVE_LIBRT)
+  if(HAVE_LIBRT)
+    list(APPEND OPENSSL_LIBRARIES rt)
+  endif()
+  check_library_exists("pthread" pthread_once "" HAVE_PTHREAD)
+  if(HAVE_PTHREAD)
+    list(APPEND OPENSSL_LIBRARIES pthread)
+  endif()
   list(APPEND CURL_LIBS ${OPENSSL_LIBRARIES})
   include_directories(${OPENSSL_INCLUDE_DIR})