Start gdb after building executable in mi-basics.exp

A lot of the MI tests start gdb and only then build the executable.
This just seemed weird to me, so I've fixed this up.  In this patch,
no other cleanups are done, the startup is just moved to a more
logical (to me) spot.

gdb/testsuite/gdb.mi/mi-basics.exp

@@ -28,11 +28,6 @@
 load_lib mi-support.exp
 set MIFLAGS "-i=mi"
 
-gdb_exit
-if [mi_gdb_start separate-inferior-tty] {
-    return
-}
-
 standard_testfile basics.c
 # This file was audited to ensure that the explicit references to
 # objdir in it are safe for parallel testing.  Please be sure to
@@ -49,6 +44,11 @@ if  { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {deb
 # In this file we want to test if the operations needed by the following
 # procedures work, so it makes no sense using them here.
 
+gdb_exit
+if [mi_gdb_start separate-inferior-tty] {
+    return
+}
+
 # mi_delete_breakpoints
 # mi_gdb_reinitialize_dir $srcdir/$subdir
 # mi_gdb_load ${binfile}