feat: update cpp-cmakefiles to 0.9.0

[devjgm]

This change is 

[coryan]

Reviewed 14 of 14 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @devbww, @mr-salty, and @scotthart)

[codecov]

Codecov Report

Merging #1489 into master will increase coverage by 0.00%.
The diff coverage is n/a.

@@ Coverage Diff @@ ## master #1489 +/- ## ======================================= Coverage 95.59% 95.59% ======================================= Files 194 193 -1 Lines 15926 15907 -19 ======================================= - Hits 15224 15207 -17  + Misses 702 700 -2 

Impacted Files	Coverage Δ
google/cloud/spanner/internal/polling_loop.h	83.33% <0.00%> (-9.53%)	⬇️
google/cloud/spanner/keys.h	100.00% <0.00%> (ø)
google/cloud/spanner/transaction.h	100.00% <0.00%> (ø)
google/cloud/spanner/internal/session.h	100.00% <0.00%> (ø)
google/cloud/spanner/session_pool_options.h	100.00% <0.00%> (ø)
google/cloud/spanner/internal/transaction_impl.h	100.00% <0.00%> (ø)
...cloud/spanner/internal/partial_result_set_resume.h	100.00% <0.00%> (ø)
.../spanner/benchmarks/multiple_rows_cpu_benchmark.cc	91.96% <0.00%> (ø)
...oogle/cloud/spanner/internal/instance_admin_stub.h
...anner/integration_tests/client_integration_test.cc	97.78% <0.00%> (+<0.01%)	⬆️
... and 5 more

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