refactor to BuildMsgOrHashOutput() #6123

Job	Run time
make check (--enable-asynccrypt-sw --enable-ocspstapling --enable-ocspstapling2 CFLAGS="-pedantic...	1m 22s
make check (--enable-ocsp CFLAGS="-DTEST_NONBLOCK_CERTS -pedantic -Wdeclaration-after-statement -...	1m 3s
make check (--enable-asynccrypt --enable-all --enable-dtls13 CFLAGS="-pedantic -Wdeclaration-afte...	2m 49s
	5m 14s

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