Fix invalid-device-fn error in cudf::strings::replace_re with multiple regex's

[davidwendt]

Found errors when testing libcudf built with gcc-9 and nvcc 11.1.

STRINGS_TEST : StringsReplaceTests.ReplaceMultiRegexTest
MERGE_TEST : MergeStringTest/8.Merge2StringKeyColumns (with BOOL8 column types only)
PARTITIONING_TEST : RoundRobinTest/8.RoundRobin (tests with BOOL8 column types only)

The strings test cause an invalid-device-function error. The code for cudf::strings::replace_re that accepts multiple regex's was fixed to better manage the device memory holding the regex structures. The error occurred when cleaning up the temporary memory.

The other two tests failed because the iterator used for generating the expected data (in CPU code) was producing the wrong results. This may be a gcc optimization bug since adding a printf cleared the error. I was able to recode the iterator's functor so it would succeed on both gcc9 and gcc7.

[codecov]

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[nvdbaranec]

edit: forgot to remove this comment. Github won't let me delete for some reason.

[harrism]

@gpucibot merge