gdb: introduce target_waitkind_str, use it in target_waitstatus::to_string

I would like to print target_waitkind values in debug messages, so I
think that a target_waitkind-to-string function would be useful.  While
at it, use it in target_waitstatus::to_string.  This changes the output
of target_waitstatus::to_string a bit, but I think it is for the better.
The debug messages will show a string matching exactly the
target_waitkind enumerator (minus the TARGET_WAITKIND prefix).

As a convenience, make string_appendf return the same reference to
string it got as a parameter.  This allows doing this:

  return string_appendf (str, "foo");

... keeping the code concise.

Change-Id: I383dffc9c78614e7d0668b1516073905e798eef7

1 files changed, 5 insertions, 2 deletions

diff --git a/gdb/unittests/common-utils-selftests.c b/gdb/unittests/common-utils-selftests.c
index 26d313f..aa0f452 100644
--- a/gdb/unittests/common-utils-selftests.c
+++ b/gdb/unittests/common-utils-selftests.c
@@ -80,7 +80,8 @@ string_vprintf_tests ()
 /* Type of both 'string_appendf' and the 'string_vappendf_wrapper'
    function below.  Used to run the same tests against both
    string_appendf and string_vappendf.  */
-typedef void (string_appendf_func) (std::string &str, const char *fmt, ...)
+typedef std::string &(string_appendf_func) (std::string &str, const char *fmt,
+					    ...)
   ATTRIBUTE_PRINTF (2, 3);
 
 static void
@@ -101,7 +102,7 @@ test_appendf_func (string_appendf_func *func)
   SELF_CHECK (str == "test23foo 45 bar");
 }
 
-static void ATTRIBUTE_PRINTF (2, 3)
+static std::string & ATTRIBUTE_PRINTF (2, 3)
 string_vappendf_wrapper (std::string &str, const char *fmt, ...)
 {
   va_list vp;
@@ -109,6 +110,8 @@ string_vappendf_wrapper (std::string &str, const char *fmt, ...)
   va_start (vp, fmt);
   string_vappendf (str, fmt, vp);
   va_end (vp);
+
+  return str;
 }
 
 static void