configure.ac: subjective simplifications
configure.ac: subjective simplifications

• avoid defining unit_test_checks, just call its body, when $enable_unit!=no

• skip the third parameter of AS_IF, if it is [].

• if the second parameter of AS_IF is [], negate the condition and remove
  the second parameter

• replace x"yes" with xyes

Signed-Off-By: Дилян Палаузов <2be63d7079beb04b5bfbe9a680bd5e7cbfcb4e9d@aegee.org>

01org/tpm2.0-tools,01org/tpm2.0-tools,01org/tpm2.0-tools