Fix GMock linkage error on Windows (#633)

Fix GMock linkage error on Windows.

Author: maxgolov

exporters/otlp/CMakeLists.txt

@@ -33,7 +33,14 @@ if(BUILD_TESTING)
     TARGET recordable_test
     TEST_PREFIX exporter.otlp.
     TEST_LIST recordable_test)
-  find_library(GMOCK_LIB gmock PATH_SUFFIXES lib)
+  if(MSVC)
+    add_definitions(-DGTEST_LINKED_AS_SHARED_LIBRARY=1)
+  endif()
+  if(MSVC AND CMAKE_BUILD_TYPE STREQUAL "Debug")
+    find_library(GMOCK_LIB gmockd PATH_SUFFIXES lib)
+  else()
+    find_library(GMOCK_LIB gmock PATH_SUFFIXES lib)
+  endif()
   if(GMOCK_LIB)
     add_executable(otlp_exporter_test test/otlp_exporter_test.cc)
     target_link_libraries(