build(c): fix warnings for MSVC (#1600) #168

Job	Run time
check (macOS, adbcdrivermanager) / r-check	3m 12s
check (macOS, adbcflightsql) / r-check	3m 10s
check (macOS, adbcpostgresql) / r-check	3m 7s
check (macOS, adbcsnowflake) / r-check	3m 11s
check (ubuntu, adbcdrivermanager) / r-check	1m 39s
check (macOS, adbcsqlite) / r-check	2m 52s
check (ubuntu, adbcflightsql) / r-check	3m 13s
check (ubuntu, adbcpostgresql) / r-check	2m 27s
check (ubuntu, adbcsnowflake) / r-check	2m 55s
check (ubuntu, adbcsqlite) / r-check	1m 58s
check (windows, adbcdrivermanager) / r-check	3m 16s
check (windows, adbcpostgresql) / r-check	3m 3s
check (windows, adbcflightsql) / r-check	3m 15s
check (windows, adbcsnowflake) / r-check	3m 11s
check (windows, adbcsqlite) / r-check	3m 15s
	43m 44s

Provide feedback