Mark more constants readonly

[Bernd Schmidt <bernds at codesourcery dot com>]

I noticed that string constants built by the Fortran frontend don't set 
TREE_READONLY for STRING_CST (and subsequently noticed that nothing 
seems to set it for COMPLEX_CST). That was confusing the ptx backend I'm 
working on.
The -fwritable-strings option for C was removed a while ago, so I tested 
the following patch to just set the flag unconditionally, and passed 
bootstrap and test on x86_64-linux. Ok?


Bernd

	* tree.c (build_string, build_complex): Set TREE_READONLY.

diff --git a/gcc/tree.c b/gcc/tree.c
index 22b92f3..067f15a 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -1755,6 +1755,7 @@ build_string (int len, const char *str)
   memset (s, 0, sizeof (struct tree_typed));
   TREE_SET_CODE (s, STRING_CST);
   TREE_CONSTANT (s) = 1;
+  TREE_READONLY (s) = 1;
   TREE_STRING_LENGTH (s) = len;
   memcpy (s->string.str, str, len);
   s->string.str[len] = '\0';
@@ -1776,6 +1777,7 @@ build_complex (tree type, tree real, tree imag)
   TREE_IMAGPART (t) = imag;
   TREE_TYPE (t) = type ? type : build_complex_type (TREE_TYPE (real));
   TREE_OVERFLOW (t) = TREE_OVERFLOW (real) | TREE_OVERFLOW (imag);
+  TREE_READONLY (t) = 1;
   return t;
 }