CMake: Exclude test-related depends when building tests

When building without tests, GTest and GMock are not needed. This change
allows build systems to continue with filecoin compilation without devoting
resources to its testing infrastructure.

Author: Garrett Brown

cmake/dependencies.cmake

@@ -1,9 +1,11 @@
 # hunter dependencies
 # https://docs.hunter.sh/en/latest/packages/
 
-# https://docs.hunter.sh/en/latest/packages/pkg/GTest.html
-hunter_add_package(GTest)
-find_package(GTest CONFIG REQUIRED)
+if (TESTING)
+  # https://docs.hunter.sh/en/latest/packages/pkg/GTest.html
+  hunter_add_package(GTest)
+  find_package(GTest CONFIG REQUIRED)
+endif()
 
 hunter_add_package(libarchive)
 find_package(libarchive CONFIG REQUIRED)