try this

Author: kkloberdanz

src/libbson/tests/test-json.c

@@ -2120,7 +2120,7 @@ test_bson_json_double (void)
    ASSERT_CMPDOUBLE (bson_iter_double (&iter), ==, 0.0);
 
 /* check that "x" is -0.0. signbit not available on Solaris or VS 2010 */
-#if !defined(__sun) && (!defined(_MSC_VER) || (_MSC_VER >= 1800))
+#if !defined(__sun) && !defined(__FreeBSD__) && (!defined(_MSC_VER) || (_MSC_VER >= 1800))
    BSON_ASSERT (signbit (bson_iter_double (&iter)));
 #endif
 

src/libmongoc/CMakeLists.txt

@@ -395,7 +395,6 @@ if (ENABLE_SHM_COUNTERS STREQUAL "ON")
    find_library(RT_LIBRARY rt HINTS /usr/lib32)
    if (RT_LIBRARY)
       set (SHM_LIBRARIES rt)
-      set (SHM_LIBRARIES m)
    endif ()
 endif ()