Use Windows symbol APIs in the unwind tester.

This should make things a bit easier to debug.

Update-Note: Test binaries on Windows now link to dbghelp.
Bug: 259
Change-Id: I9da1fc89d429080c5250238e4341445922b1dd8e
Reviewed-on: https://boringssl-review.googlesource.com/c/34868
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
diff --git a/crypto/test/CMakeLists.txt b/crypto/test/CMakeLists.txt
index d2e4cdf..b968fd7 100644
--- a/crypto/test/CMakeLists.txt
+++ b/crypto/test/CMakeLists.txt
@@ -15,6 +15,9 @@
   target_include_directories(test_support_lib PRIVATE ${LIBUNWIND_INCLUDE_DIRS})
   target_link_libraries(test_support_lib ${LIBUNWIND_LDFLAGS})
 endif()
+if(WIN32)
+  target_link_libraries(test_support_lib dbghelp)
+endif()
 add_dependencies(test_support_lib global_target)
 
 add_library(