libctf: a little string sharing test

It's actually quite hard to come up with simple tests that do *not* share
all their strings, but with enough ingenuity suitable cycles can be
concocted.

This test verifies that only and precisely those strings that are only used
in one child dict actually end up in its strtab.

ld/
	* testsuite/ld-ctf/unshared-strings*: New test.

ld/testsuite/ld-ctf/unshared-strings-A.c

@@ -0,0 +1,19 @@
+struct A;
+struct B
+{
+  int foo;
+  struct A *a;
+};
+struct C;
+typedef struct C aaa;
+struct A
+{
+  aaa *wurblefrotz;
+};
+struct C
+{
+  struct B *foo;
+};
+
+static struct A *foo __attribute__((used));
+

ld/testsuite/ld-ctf/unshared-strings-B.c

@@ -0,0 +1,21 @@
+struct A;
+struct B
+{
+  int foo;
+  struct A *a;
+};
+struct C;
+typedef struct C C1;
+typedef C1 C2;
+struct A
+{
+  C2 *wurblefritz;
+};
+
+struct C
+{
+  struct B *foo;
+};
+
+static struct A *foo __attribute__((used));
+

ld/testsuite/ld-ctf/unshared-strings.d

@@ -0,0 +1,45 @@
+#as:
+#source: unshared-strings-A.c
+#source: unshared-strings-B.c
+#objdump: --ctf
+#ld: -shared
+#name: Verify proper sharing (and non-sharing) of strings
+
+.*: +file format .*
+
+Contents of CTF section .ctf:
+
+  Header:
+    Magic number: 0xdff2
+    Version: 5 \(CTF_VERSION_4\)
+#...
+  Strings:
+    0x0: 
+    0x[0-9a-f]*: A
+#...
+    0x[0-9a-f]*: C1
+    0x[0-9a-f]*: C2
+#...
+    0x[0-9a-f]*: aaa
+#...
+CTF archive member: .*/unshared-strings-A.c:
+#...
+  Types:
+    0x[0-9a-f]*: \(kind 6\) struct A .*
+                \[0x0\] wurblefrotz: ID .*
+
+  Strings:
+    0x0: .ctf
+#...
+    0x[0-9a-f]*: wurblefrotz
+
+CTF archive member: .*/unshared-strings-B.c:
+#...
+  Types:
+    0x[0-9a-f]*: \(kind 6\) struct A .*
+                \[0x0\] wurblefritz: ID .*
+
+  Strings:
+    0x0: .ctf
+#...
+    0x[0-9a-f]*: wurblefritz