gdb/testsuite: explicitly test for stderr in gdb.mi/mi-dprintf.exp

As mentioned in commit 3f5bbc3e20, some
compilers such as clang don't add debug information about stderr by
default, leaving it to external debug packages.

This commit adds a way to check if GDB has access to stderr information
when in MI mode, and uses this new mechanism to skip the related section
of the test gdb.mi/mi-dprintf.exp. It also fixes an incorrect name for a
test in that file.

Co-Authored-By: Andrew Burgess <aburgess@redhat.com>
Approved-By: Kevin Buettner <kevinb@redhat.com>

gdb/testsuite/gdb.mi/mi-dprintf.exp

@@ -127,6 +127,7 @@ proc mi_continue_dprintf {args} {
 mi_continue_dprintf "gdb"
 
 # The "call" style depends on having I/O functions available, so test.
+set has_stderr_symbol [mi_gdb_is_stderr_available]
 
 if ![target_info exists gdb,noinferiorio] {
 
@@ -136,9 +137,13 @@ if ![target_info exists gdb,noinferiorio] {
     mi_gdb_test "set dprintf-style call" ".*" "mi set dprintf style to call"
     mi_continue_dprintf "call"
 
-    mi_gdb_test "set dprintf-function fprintf" ".*" "mi set dprintf-channel stderr"
-    mi_gdb_test "set dprintf-channel stderr" ".*" "mi set dprintf channel"
-    mi_continue_dprintf "fprintf"
+    # Some compilers don't add information about stderr,
+    # so skip these tests if needed.
+    if {$::has_stderr_symbol} {
+	mi_gdb_test "set dprintf-function fprintf" ".*" "mi set dprintf function"
+	mi_gdb_test "set dprintf-channel stderr" ".*" "mi set dprintf channel"
+	mi_continue_dprintf "fprintf"
+    }
 }
 
 set target_can_dprintf 0

gdb/testsuite/lib/mi-support.exp

@@ -2942,3 +2942,17 @@ proc foreach_mi_ui_mode { var_name body } {
        }
     }
 }
+
+# Check if GDB has information about the stderr symbol.
+proc mi_gdb_is_stderr_available {} {
+    set has_stderr_symbol false
+    gdb_test_multiple "-data-evaluate-expression stderr" "stderr symbol check" {
+	-re "\\^error,msg=\"'stderr' has unknown type; cast it to its declared type\"\r\n$::mi_gdb_prompt$" {
+	    # Default value of false is fine.
+	}
+	-re "$::mi_gdb_prompt$" {
+	    set has_stderr_symbol true
+	}
+    }
+    return $has_stderr_symbol
+}