Build breaks for GCC 4.8

Job #1996 failed for a2d8277d:

In file included from ../../src/rpcs.cpp:40:0:
../../src/rpcs.hpp:54:21: error: field initializer is not constant
     hermes::detail::hg_proc_ ## struct_type_name
                     ^
../../src/rpcs.hpp:150:9: note: in expansion of macro 'HG_GEN_PROC_NAME'
         HG_GEN_PROC_NAME(push_resource_in_t);
         ^
../../src/rpcs.hpp:54:21: error: field initializer is not constant
     hermes::detail::hg_proc_ ## struct_type_name
                     ^
../../src/rpcs.hpp:154:9: note: in expansion of macro 'HG_GEN_PROC_NAME'
         HG_GEN_PROC_NAME(push_resource_out_t);
         ^
../../src/rpcs.hpp:54:21: error: field initializer is not constant
     hermes::detail::hg_proc_ ## struct_type_name
                     ^
../../src/rpcs.hpp:478:9: note: in expansion of macro 'HG_GEN_PROC_NAME'
         HG_GEN_PROC_NAME(pull_resource_in_t);
         ^
../../src/rpcs.hpp:54:21: error: field initializer is not constant
     hermes::detail::hg_proc_ ## struct_type_name
                     ^
../../src/rpcs.hpp:482:9: note: in expansion of macro 'HG_GEN_PROC_NAME'
         HG_GEN_PROC_NAME(pull_resource_out_t);
         ^
../../src/rpcs.hpp:54:21: error: field initializer is not constant
     hermes::detail::hg_proc_ ## struct_type_name
                     ^
../../src/rpcs.hpp:786:9: note: in expansion of macro 'HG_GEN_PROC_NAME'
         HG_GEN_PROC_NAME(stat_resource_in_t);
         ^
../../src/rpcs.hpp:54:21: error: field initializer is not constant
     hermes::detail::hg_proc_ ## struct_type_name
                     ^
../../src/rpcs.hpp:790:9: note: in expansion of macro 'HG_GEN_PROC_NAME'
         HG_GEN_PROC_NAME(stat_resource_out_t);