Update tools/checkstack.py - new compilers set %ebp in preamble.

A 'movl   %esp,%ebp' can occur in the preamble - note for proper stack
    usage checking.
diff --git a/tools/checkstack.py b/tools/checkstack.py
index aa38ea8..82becdd 100755
--- a/tools/checkstack.py
+++ b/tools/checkstack.py
@@ -78,6 +78,9 @@
                 stackusage += int(im.group('num'), 16)
 
             if atstart:
+                if insn == 'movl   %esp,%ebp':
+                    # Still part of initial header
+                    continue
                 cur[1] = stackusage
                 atstart = 0