Allow the function to be individually linkable, discardable, and
overridable. In fact the function is unused at present, and hence will
now get omitted from the final binaries.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/common/string.c
+++ b/xen/common/string.c
@@ -8,33 +8,6 @@
 #include <xen/string.h>
 #include <xen/ctype.h>
 
-#ifndef __HAVE_ARCH_STRSPN
-/**
- * strspn - Calculate the length of the initial substring of @s which only
- * 	contain letters in @accept
- * @s: The string to be searched
- * @accept: The string to search for
- */
-size_t strspn(const char *s, const char *accept)
-{
-	const char *p;
-	const char *a;
-	size_t count = 0;
-
-	for (p = s; *p != '\0'; ++p) {
-		for (a = accept; *a != '\0'; ++a) {
-			if (*p == *a)
-				break;
-		}
-		if (*a == '\0')
-			return count;
-		++count;
-	}
-
-	return count;
-}
-#endif
-
 #ifndef __HAVE_ARCH_STRPBRK
 /**
  * strpbrk - Find the first occurrence of a set of characters
--- a/xen/lib/Makefile
+++ b/xen/lib/Makefile
@@ -24,6 +24,7 @@ lib-y += strncasecmp.o
 lib-y += strncmp.o
 lib-y += strnlen.o
 lib-y += strrchr.o
+lib-y += strspn.o
 lib-y += strstr.o
 lib-$(CONFIG_X86) += xxhash32.o
 lib-$(CONFIG_X86) += xxhash64.o
--- /dev/null
+++ b/xen/lib/strspn.c
@@ -0,0 +1,40 @@
+/*
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ */
+
+#include <xen/string.h>
+
+/**
+ * strspn - Calculate the length of the initial substring of @s which only
+ * 	contain letters in @accept
+ * @s: The string to be searched
+ * @accept: The string to search for
+ */
+size_t strspn(const char *s, const char *accept)
+{
+	const char *p;
+	const char *a;
+	size_t count = 0;
+
+	for (p = s; *p != '\0'; ++p) {
+		for (a = accept; *a != '\0'; ++a) {
+			if (*p == *a)
+				break;
+		}
+		if (*a == '\0')
+			return count;
+		++count;
+	}
+
+	return count;
+}
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 8
+ * tab-width: 8
+ * indent-tabs-mode: t
+ * End:
+ */