Otherwise a smaller type may be promoted to int, which can hit undefined
behaviour:

../src/intel/compiler/brw_packed_float.c:66:17: runtime error: left shift of 128 by 24 places cannot be represented in type 'int'
    #0 0x5604a03969aa in brw_vf_to_float ../src/intel/compiler/brw_packed_float.c:66
    #1 0x5604a0391305 in vf_float_conversion_test_test_vf_to_float_Test::TestBody() ../src/intel/compiler/test_vf_float_conversions.cpp:70
    #2 0x5604a041a323 in void testing::internal::HandleSehExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ../src/gtest/src/gtest.cc:2402
    #3 0x5604a0405c31 in void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*) ../src/gtest/src/gtest.cc:2438
    #4 0x5604a03ab03b in testing::Test::Run() ../src/gtest/src/gtest.cc:2474
    #5 0x5604a03ad714 in testing::TestInfo::Run() ../src/gtest/src/gtest.cc:2656
    #6 0x5604a03afea2 in testing::TestCase::Run() ../src/gtest/src/gtest.cc:2774
    #7 0x5604a03cb87c in testing::internal::UnitTestImpl::RunAllTests() ../src/gtest/src/gtest.cc:4649
    #8 0x5604a041df3c in bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) ../src/gtest/src/gtest.cc:2402
    #9 0x5604a0409609 in bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) ../src/gtest/src/gtest.cc:2438
    #10 0x5604a03c2e9e in testing::UnitTest::Run() ../src/gtest/src/gtest.cc:4257
    #11 0x5604a0442d57 in RUN_ALL_TESTS() ../src/gtest/include/gtest/gtest.h:2233
    #12 0x5604a0442c17 in main ../src/gtest/src/gtest_main.cc:37
    #13 0x7f9a1983dbba in __libc_start_main ../csu/libc-start.c:308
    #14 0x5604a0390d89 in _start (/home/daenzer/src/mesa-git/mesa/build-amd64-sanitize/src/intel/compiler/vf_float_conversions+0x8dd89)

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Adam Jackson <ajax@redhat.com>