tools lib: Adopt strim() from the kernel

Since we're working on moving stuff out of tools/perf/util/ to
tools/lib/, take the opportunity to adopt routines from the kernel that
are equivalent, so that tools/ code look more like the kernel.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: André Goddard Rosa <andre.goddard@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-zqy1zdu2ok17qvi0ytk8z13c@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/include/linux/string.h

@@ -31,4 +31,6 @@ static inline bool strstarts(const char *str, const char *prefix)
 
 extern char * __must_check skip_spaces(const char *);
 
+extern char *strim(char *);
+
 #endif /* _TOOLS_LINUX_STRING_H_ */

tools/lib/string.c

@@ -120,3 +120,28 @@ char *skip_spaces(const char *str)
 		++str;
 	return (char *)str;
 }
+
+/**
+ * strim - Removes leading and trailing whitespace from @s.
+ * @s: The string to be stripped.
+ *
+ * Note that the first trailing whitespace is replaced with a %NUL-terminator
+ * in the given string @s. Returns a pointer to the first non-whitespace
+ * character in @s.
+ */
+char *strim(char *s)
+{
+	size_t size;
+	char *end;
+
+	size = strlen(s);
+	if (!size)
+		return s;
+
+	end = s + size - 1;
+	while (end >= s && isspace(*end))
+		end--;
+	*(end + 1) = '\0';
+
+	return skip_spaces(s);
+}