devel/aws-c-common: port improvements

• Define LICENSE_FILE
• Use ports framework for unit testing
• Use CMake helpers provided by framework
• Remove unneeded CFLAGS+=-DBSD_VISIBLE=1 since: ${WRKSRC}/source/posix/system_info.c: --- #if defined(FreeBSD) || defined(NetBSD__)
  1. define __BSD_VISIBLE 1 #endif ---
• Not bumping PORTREVISION

PR: 266405