[cmdline] Show commands in alphabetical order

Commands were originally ordered by functional group (e.g. keeping the
image management commands together), with arrays used to impose a
functionally meaningful order within the group.

As the number of commands and functional groups has expanded over the
years, this has become essentially useless as an organising principle.
Switch to sorting commands alphabetically (using the linker table
mechanism).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/exec.c

@@ -428,10 +428,7 @@ static int echo_exec ( int argc, char **argv ) {
 }
 
 /** "echo" command */
-struct command echo_command __command = {
-	.name = "echo",
-	.exec = echo_exec,
-};
+COMMAND ( echo, echo_exec );
 
 /** "exit" options */
 struct exit_options {};
@@ -472,10 +469,7 @@ static int exit_exec ( int argc, char **argv ) {
 }
 
 /** "exit" command */
-struct command exit_command __command = {
-	.name = "exit",
-	.exec = exit_exec,
-};
+COMMAND ( exit, exit_exec );
 
 /** "isset" options */
 struct isset_options {};
@@ -507,10 +501,7 @@ static int isset_exec ( int argc, char **argv ) {
 }
 
 /** "isset" command */
-struct command isset_command __command = {
-	.name = "isset",
-	.exec = isset_exec,
-};
+COMMAND ( isset, isset_exec );
 
 /** "iseq" options */
 struct iseq_options {};
@@ -544,10 +535,7 @@ static int iseq_exec ( int argc, char **argv ) {
 }
 
 /** "iseq" command */
-struct command iseq_command __command = {
-	.name = "iseq",
-	.exec = iseq_exec,
-};
+COMMAND ( iseq, iseq_exec );
 
 /** "sleep" options */
 struct sleep_options {};
@@ -587,7 +575,4 @@ static int sleep_exec ( int argc, char **argv ) {
 }
 
 /** "sleep" command */
-struct command sleep_command __command = {
-	.name = "sleep",
-	.exec = sleep_exec,
-};
+COMMAND ( sleep, sleep_exec );