enable tests in getdeps

Summary:
in getdeps we currently don't build and run the tests
There are a few issues:
  1. we need to also build tests for fizz, wangle, mvfst since proxygen tests include headers only exported if building tests in dependencies
  2. we use `ExternalProject_add` for gtest/gmock. but doesn't seem to be playing nicely with getdeps

Reviewed By: dddmello, mjoras

Differential Revision: D16934955

fbshipit-source-id: fb1c52237f9f0c71da86643409972c94d16e6a71

build/fbcode_builder/manifests/proxygen

@@ -15,8 +15,13 @@ builder = cmake
 subdir = .
 
 [cmake.defines]
-BUILD_QUIC=ON
-BUILD_TESTS=OFF
+BUILD_QUIC = ON
+
+[cmake.defines.test=on]
+BUILD_TESTS = ON
+
+[cmake.defines.test=off]
+BUILD_TESTS = OFF
 
 [dependencies]
 gperf
@@ -24,6 +29,7 @@ folly
 fizz
 wangle
 mvfst
+googletest_1_8
 
 [shipit.pathmap]
 fbcode/proxygen/public_tld = .