meson, configure: move --with-pkgversion, CONFIG_STAMP to meson

The hash is now generated with a Python script.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

scripts/qemu-stamp.py

@@ -0,0 +1,24 @@
+#! /usr/bin/env python3
+
+# Usage: scripts/qemu-stamp.py STRING1 STRING2... -- FILE1 FILE2...
+import hashlib
+import os
+import sys
+
+sha = hashlib.sha1()
+is_file = False
+for arg in sys.argv[1:]:
+    if arg == '--':
+        is_file = True
+        continue
+    if is_file:
+        with open(arg, 'rb') as f:
+            for chunk in iter(lambda: f.read(65536), b''):
+                sha.update(chunk)
+    else:
+        sha.update(os.fsencode(arg))
+        sha.update(b'\n')
+
+# The hash can start with a digit, which the compiler doesn't
+# like as an symbol. So prefix it with an underscore
+print("_" + sha.hexdigest())