re_cpp matches are never empty

tests/preproc/src/main.c

@@ -1,7 +1,11 @@
 
 #if A
+const char* c = "foo /*";
   #if B
+const char* d = " bar */";
+// /*
     #if C
+// */
       #include "a.h"
     #else
       #include "b.h"

waflib/Tools/c_preproc.py

@@ -138,7 +138,7 @@ skipped   = 's'
 def repl(m):
 	"""Replace function used with :py:attr:`waflib.Tools.c_preproc.re_cpp`"""
 	s = m.group(0)
-	if s.startswith('/'):
+	if s[0] == '/':
 		return ' '
 	return s