[gdb/testsuite] Don't pass/fail in gnat_runtime_has_debug_info

After de-installing gnatmake, I get:
...
Running src/gdb/testsuite/gdb.base/gdb-caching-proc.exp ...
FAIL: gdb-caching-proc.exp: failed to compile gnat-debug-info test binary
  ...
FAIL: gdb-caching-proc.exp: failed to compile gnat-debug-info test binary
...

In gdb.sum, we see these FAILs (each paired with an UNSUPPORTED as well)
followed by:
...
PASS: gdb-caching-proc.exp: gnat_runtime_has_debug_info consistency
...

Fix this by removing the fail calls in gnat_runtime_has_debug_info, as well
as using a new variant gdb_compile_ada_1 that doesn't call pass.

Tested on x86_64-linux, with gnatmake installed and de-installed.

gdb/testsuite/ChangeLog:

2020-02-18  Tom de Vries  <tdevries@suse.de>

	* lib/ada.exp (gdb_compile_ada_1): Factor out of ...
	(gdb_compile_ada): ... here.
	(gnat_runtime_has_debug_info): Remove fail calls.  Use
	gdb_compile_ada_1 instead of gdb_compile_ada.

---
 gdb/testsuite/lib/ada.exp | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/gdb/testsuite/lib/ada.exp b/gdb/testsuite/lib/ada.exp
index 9933cc951e..0689eeb239 100644
--- a/gdb/testsuite/lib/ada.exp
+++ b/gdb/testsuite/lib/ada.exp
@@ -52,9 +52,9 @@ proc target_compile_ada_from_dir {builddir source dest type options} {
     return -options $options $result
 }
 
-# Compile some Ada code.
+# Compile some Ada code.  Return "" if the compile was successful.
 
-proc gdb_compile_ada {source dest type options} {
+proc gdb_compile_ada_1 {source dest type options} {
 
     set srcdir [file dirname $source]
     set gprdir [file dirname $srcdir]
@@ -80,6 +80,15 @@ proc gdb_compile_ada {source dest type options} {
     # We therefore simply check whether the dest file has been created
     # or not. Unless not present, the build has succeeded.
     if [file exists $dest] { set result "" }
+    return $result
+}
+
+# Compile some Ada code.  Generate "PASS: foo.exp: compilation SOURCE" if the
+# compile was successful.
+
+proc gdb_compile_ada {source dest type options} {
+    set result [gdb_compile_ada_1 $source $dest $type $options]
+
     gdb_compile_test $source $result
     return $result
 }
@@ -162,15 +171,13 @@ gdb_caching_proc gnat_runtime_has_debug_info {
     set src "$srcdir/lib/gnat_debug_info_test.adb"
     set dst [standard_output_file "gnat_debug_info_test"]
 
-    if { [gdb_compile_ada $src $dst executable {debug}] != "" } {
-	fail "failed to compile gnat-debug-info test binary"
+    if { [gdb_compile_ada_1 $src $dst executable {debug}] != "" } {
 	return 0
     }
 
     clean_restart $dst
 
     if { ! [runto "GNAT_Debug_Info_Test"] } {
-	fail "failed to run to GNAT_Debug_Info_Test"
 	return 0
     }
 
@@ -183,7 +190,6 @@ gdb_caching_proc gnat_runtime_has_debug_info {
 	}
 	default {
 	    # Some other unexpected output...
-	    fail $gdb_test_name
 	}
     }