Exclude c_test from buck build opt mode (#7093)

Summary:
Fix a Facebook internal build

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7093

Test Plan:
buck build mode/opt :c_test :c_test_bin (was compilation
failure, now "not found")
buck build mode/dev :c_test :c_test_bin (still passes)

Reviewed By: ajkr

Differential Revision: D22412528

Pulled By: pdillinger

fbshipit-source-id: 8e55c43dbf95386597e4cc690c41d9cbdcee03aa

TARGETS

@@ -449,6 +449,7 @@ cpp_library(
     external_deps = ROCKSDB_EXTERNAL_DEPS,
 )
 
+if not is_opt_mode:
     cpp_binary(
         name = "c_test_bin",
         srcs = ["db/c_test.c"],
@@ -459,6 +460,7 @@ cpp_binary(
         deps = [":rocksdb_test_lib"],
     )
 
+if not is_opt_mode:
     custom_unittest(
         "c_test",
         command = [

buckifier/targets_builder.py

@@ -78,6 +78,7 @@ class TARGETSBuilder(object):
 
     def add_c_test(self):
         self.targets_file.write("""
+if not is_opt_mode:
     cpp_binary(
         name = "c_test_bin",
         srcs = ["db/c_test.c"],
@@ -88,6 +89,7 @@ cpp_binary(
         deps = [":rocksdb_test_lib"],
     )
 
+if not is_opt_mode:
     custom_unittest(
         "c_test",
         command = [