Build gbc without optimization inside Travis

We've been seeing timeouts building gbc on the Travis infrastructure.
Building without optimizations reduces the build time significantly and
shouldn't affect build or test results.

Closes https://github.com/Microsoft/bond/issues/176, "ghc 7.8.4 OS X
Travis CI builds are failing"

Closes https://github.com/Microsoft/bond/pull/195, "Build gbc without
optimization inside Travis"

compiler/cabal_build.cmake

@@ -42,8 +42,17 @@ if (error)
     message (FATAL_ERROR)
 endif()
 
+set (buildGhcOptions "-O2")
+
+if ($ENV{TRAVIS})
+    # We've been seeing timeouts building gbc on the Travis infrastructure.
+    # Building without optimizations reduces the build time significantly
+    # and shouldn't affect build or test results.
+    set (buildGhcOptions "-O0")
+endif()
+
 execute_process (
-    COMMAND ${Haskell_CABAL_EXECUTABLE} build ${target} --with-ghc=${Haskell_GHC_EXECUTABLE} --ghc-option=-O2 --jobs --builddir=${build_dir}
+    COMMAND ${Haskell_CABAL_EXECUTABLE} build ${target} --with-ghc=${Haskell_GHC_EXECUTABLE} --ghc-option=${buildGhcOptions} --jobs --builddir=${build_dir}
     WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
     RESULT_VARIABLE error)