MDEV-35850 make HOSTNAME a cmake configure variable

As seen with openwrt and some other distros, the
determination of hostname can sometime need alternate
commmands.

This provides a cmake option HOSTNAME for non-windows machines
for the mariadb-install-db and mariadbd-safe scripts
and the support-files init scripts..

CMakeLists.txt

@@ -379,6 +379,7 @@ IF(WIN32)
 ELSE()
   SET(DEFAULT_MYSQL_HOME ${CMAKE_INSTALL_PREFIX})
   SET(SHAREDIR ${INSTALL_MYSQLSHAREDIRABS})
+  SET(HOSTNAME "uname -n" CACHE STRING "Command for determining hostname")
 ENDIF()
 
 SET(DEFAULT_BASEDIR "${DEFAULT_MYSQL_HOME}")

scripts/CMakeLists.txt

@@ -177,7 +177,6 @@ ELSE()
   SET(CHECK_PID "kill -s SIGCONT $PID  > /dev/null 2> /dev/null")
 ENDIF()
 
-SET(HOSTNAME "uname -n")
 SET(MYSQLD_USER "mysql")
 SET(MYSQLD_GROUP "mysql")
 ENDIF(UNIX)

support-files/CMakeLists.txt

@@ -31,7 +31,6 @@ ELSE()
   SET(MYSQLD_USER "mysql")
   SET(MYSQLD_GROUP "mysql")
   SET(ini_file_extension "cnf")
-  SET(HOSTNAME "uname -n")
 
   # Define directly here, as cmake/install_layout.cmake has no LOGDIR to be inherited
   SET(su_user "su mysql mysql")