Skip testing argv[0] on target argv[0] isn't available

I see the following two fails on arm-none-eabi target, because argv[0]
isn't available.

print argv[0]^M
$1 = 0x1f78 "/dev/null"^M
(gdb) FAIL: gdb.base/argv0-symlink.exp: kept file symbolic link name

print argv[0]^M
$1 = 0x1f78 "/dev/null"^M
(gdb) FAIL: gdb.base/argv0-symlink.exp: kept directory symbolic link name

My first thought is to check [target_info exists noargs], and skip the
test if it returns true.  However, noargs is set in gdbserver board
files, so argv0-symlink.exp will be skipped on gdbserver board file.
The change is too aggressive.

When the program is running with gdbserver, argv[1] to argv[N] aren't
available, but argv[0] is.  Fortunately, argv0-symlink.exp only
requires argv[0].  argv0-symlink.exp can be run with gdbserver board
file, as what we do now.

What we need to check is whether argv[0] is available, so I add a new
proc gdb_has_argv0 to do so by starting a program, and check
argc/argv[0] to see whether argv[0] is available.

Dan fixed the similar problem by checking noargs, which is too strong.
https://sourceware.org/ml/gdb-patches/2010-02/msg00398.html as a
result, the test is skipped on gdbserver.  This patch fixed it too.

gdb/testsuite:

2014-10-18  Yao Qi  <yao@codesourcery.com>

	* gdb.base/argv0-symlink.exp: Check argv[0] value if
	gdb_has_argv0 return true.
	* gdb.guile/scm-value.exp (test_value_in_inferior): Don't
	check [target_info exists noargs], check [gdb_has_argv0]
	instead.
	* gdb.python/py-value.exp (test_value_in_inferior): Likewise.
	* lib/gdb.exp (gdb_has_argv0, gdb_has_argv0_1): New
	procedures.

1 files changed, 8 insertions, 3 deletions

diff --git a/gdb/testsuite/gdb.guile/scm-value.exp b/gdb/testsuite/gdb.guile/scm-value.exp
index ae80d1b..033633c 100644
--- a/gdb/testsuite/gdb.guile/scm-value.exp
+++ b/gdb/testsuite/gdb.guile/scm-value.exp
@@ -20,6 +20,8 @@ load_lib gdb-guile.exp
 
 standard_testfile
 
+set has_argv0 [gdb_has_argv0]
+
 # Build inferior to language specification.
 # LANG is one of "c" or "c++".
 proc build_inferior {exefile lang} {
@@ -86,9 +88,12 @@ proc test_value_in_inferior {} {
 	"set arg0"
 
     # Check that the dereferenced value is sane.
-    if { ! [target_info exists noargs] } {
-	gdb_test "gu (print arg0)" \
-	    "0x.*$testfile\"" "verify dereferenced value"
+    global has_argv0
+    set test "verify dereferenced value"
+    if { $has_argv0 } {
+	gdb_test "gu (print arg0)" "0x.*$testfile\"" $test
+    } else {
+	unsupported $test
     }
 
     # Smoke-test value-optimized-out?.