Issue #132 Proper googletest dependency and fixes for unitests on OSX.

Problem:
It's really hard to get Libuavcan tests building on a mac or other platform if googletest isn't installed.

Solution:
add "if linux" guards to problem areas. Also include googletest as recommended in the googletest project's README.

Testing:
Successfully built on OSX sierra using gcc6

libuavcan/CMakeLists.txt

@@ -89,7 +89,6 @@ install(CODE "execute_process(COMMAND ${PYTHON} setup.py install --record instal
 #
 function(add_libuavcan_test name library flags) # Adds GTest executable and creates target to execute it every build
     find_package(Threads REQUIRED)
-    include_directories(${GTEST_INCLUDE_DIRS})
 
     file(GLOB_RECURSE TEST_CXX_FILES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "test/*.cpp")
     add_executable(${name} ${TEST_CXX_FILES})
@@ -99,9 +98,11 @@ function(add_libuavcan_test name library flags) # Adds GTest executable and crea
         set_target_properties(${name} PROPERTIES COMPILE_FLAGS ${flags})
     endif ()
 
-    target_link_libraries(${name} ${GTEST_BOTH_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT})
+    target_link_libraries(${name} gmock_main)
     target_link_libraries(${name} ${library})
-    target_link_libraries(${name} rt)
+    if (${UAVCAN_PLATFORM} STREQUAL "linux")
+        target_link_libraries(${name} rt)
+    endif()
 
     # Tests run automatically upon successful build
     # If failing tests need to be investigated with debugger, use 'make --ignore-errors'
@@ -145,10 +146,8 @@ if (DEBUG_BUILD)
     set_target_properties(uavcan_optim PROPERTIES COMPILE_FLAGS ${optim_flags})
     add_dependencies(uavcan_optim libuavcan_dsdlc)
 
-    # GTest executables
-    find_package(GTest)
     if (GTEST_FOUND)
-        message(STATUS "GTest found, tests will be built and run [${GTEST_INCLUDE_DIRS}] [${GTEST_BOTH_LIBRARIES}]")
+        message(STATUS "GTest found, tests will be built and run.")
         add_libuavcan_test(libuavcan_test       uavcan       "")                 # Default
         add_libuavcan_test(libuavcan_test_cpp03 uavcan_cpp03 "${cpp03_flags}")   # C++03
         add_libuavcan_test(libuavcan_test_optim uavcan_optim "${optim_flags}")   # Max optimization

libuavcan/test/helpers/heap_based_pool_allocator.cpp

@@ -4,13 +4,19 @@
 
 #include <gtest/gtest.h>
 #include <uavcan/helpers/heap_based_pool_allocator.hpp>
+#ifdef __linux__
 #include <malloc.h>
 
+#else
+#include <stdlib.h>
+#endif
 
 TEST(HeapBasedPoolAllocator, Basic)
 {
+#ifdef __linux__
     std::cout << ">>> HEAP BEFORE:" << std::endl;
     malloc_stats();
+#endif
 
     uavcan::HeapBasedPoolAllocator<uavcan::MemPoolBlockSize> al(0xEEEE);
 
@@ -61,8 +67,10 @@ TEST(HeapBasedPoolAllocator, Basic)
     ASSERT_EQ(0, al.getNumReservedBlocks());
     ASSERT_EQ(0, al.getNumAllocatedBlocks());
 
+#ifdef __linux__
     std::cout << ">>> HEAP AFTER:" << std::endl;
     malloc_stats();
+#endif
 }
 
 
@@ -115,9 +123,11 @@ std::mutex RaiiSynchronizer::mutex;
 
 TEST(HeapBasedPoolAllocator, Concurrency)
 {
+#ifdef __linux__
     std::cout << ">>> HEAP BEFORE:" << std::endl;
     malloc_stats();
 
+#endif
     uavcan::HeapBasedPoolAllocator<uavcan::MemPoolBlockSize, RaiiSynchronizer> al(1000);
 
     ASSERT_EQ(1000, al.getBlockCapacity());
@@ -167,13 +177,17 @@ TEST(HeapBasedPoolAllocator, Concurrency)
     std::cout << "Allocated: " << al.getNumAllocatedBlocks() << std::endl;
     std::cout << "Reserved:  " << al.getNumReservedBlocks() << std::endl;
 
+#ifdef __linux__
     std::cout << ">>> HEAP BEFORE SHRINK:" << std::endl;
     malloc_stats();
 
+#endif
     al.shrink();
 
+#ifdef __linux__
     std::cout << ">>> HEAP AFTER SHRINK:" << std::endl;
     malloc_stats();
+#endif
 }
 
 #endif