tools: cmake: link librt if needed (FS#381)

Patch cmakes cmcurl component to unconditionally link librt when we discover
a clock_gettime() symbol in -lrt.

This is required to sucessfully link LibreSSL's libcrypto which might or
might not reqauire librt.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

1 files changed, 32 insertions, 0 deletions

diff --git a/tools/cmake/patches/140-curl-fix-libressl-linking.patch b/tools/cmake/patches/140-curl-fix-libressl-linking.patch
new file mode 100644
index 0000000000..5b57172eb4
--- /dev/null
+++ b/tools/cmake/patches/140-curl-fix-libressl-linking.patch
@@ -0,0 +1,32 @@
+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
+@@ -362,6 +362,10 @@ set(HAVE_LIBSSL OFF)
+ if(CMAKE_USE_OPENSSL)
+   find_package(OpenSSL)
+   if(OPENSSL_FOUND)
++    check_library_exists("rt" clock_gettime "" HAVE_LIBRT)
++    if(HAVE_LIBRT)
++      list(APPEND OPENSSL_LIBRARIES rt)
++    endif()
+     list(APPEND CURL_LIBS ${OPENSSL_LIBRARIES})
+     set(USE_OPENSSL ON)
+     set(HAVE_LIBCRYPTO ON)