Merge pull request #1438 from delcypher/cmake_old_glibc_librt

[CMake] Fix #1437

CMakeLists.txt

@@ -257,6 +257,46 @@ list(APPEND Z3_COMPONENT_EXTRA_INCLUDE_DIRS
   "${CMAKE_BINARY_DIR}/src"
   "${CMAKE_SOURCE_DIR}/src"
 )
+
+################################################################################
+# Linux specific configuration
+################################################################################
+if ("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
+  # Try to detect if it is necessary to link against librt.
+  # Note that glibc < 2.17 required librt to be linked to use clock_gettime()
+  # and friends.
+  set(CLOCK_GETTIME_REQUIRES_LIBRT_TEST_CODE
+    "
+    #include <time.h>
+    int main() {
+      timespec res;
+      int result = clock_gettime(CLOCK_REALTIME, &res);
+      return result == 0;
+    }
+    "
+  )
+  check_cxx_source_compiles(
+    "${CLOCK_GETTIME_REQUIRES_LIBRT_TEST_CODE}"
+    CLOCK_GETTIME_NO_REQUIRE_LIBRT
+  )
+  if (NOT CLOCK_GETTIME_NO_REQUIRE_LIBRT)
+    # Try again with librt
+    message(STATUS "Failed to link against clock_gettime(), trying with librt")
+    set(CMAKE_REQUIRED_LIBRARIES_OLD "${CMAKE_REQUIRED_LIBRARIES}")
+    set(CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES} rt")
+    check_cxx_source_compiles(
+      "${CLOCK_GETTIME_REQUIRES_LIBRT_TEST_CODE}"
+      CLOCK_GETTIME_REQUIRES_LIBRT
+    )
+    set(CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_OLD}")
+    if (CLOCK_GETTIME_REQUIRES_LIBRT)
+      list(APPEND Z3_DEPENDENT_LIBS "rt")
+    else()
+      message(FATAL_ERROR "Failed to link against clock_gettime()")
+    endif()
+  endif()
+endif()
+
 ################################################################################
 # GNU multiple precision library support
 ################################################################################