[gdb/testsuite] Skip gdb.base/readnever.exp with target board readnow

When running test-case gdb.base/readnever.exp with target board readnow, we
have:
...
spawn gdb -nw -nx -data-directory data-directory -ex set sysroot -readnow \
  --readnever^M
gdb: '--readnow' and '--readnever' cannot be specified simultaneously^M
ERROR: : spawn id exp19 not open
...

Fix this by skipping the test when -readnow/--readnow is detected in
GDBFLAGS.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-04-23  Tom de Vries  <tdevries@suse.de>

	* gdb.base/readnever.exp: Skip if GDBFLAGS contain -readnow/--readnow.

2 files changed, 11 insertions, 0 deletions

diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 5700fa8..7e6bf73 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2020-04-23  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.base/readnever.exp: Skip if GDBFLAGS contain -readnow/--readnow.
+
 2020-04-22  Tom de Vries  <tdevries@suse.de>
 
 	* gdb.mi/dw2-ref-missing-frame-func.c (.debug_aranges): Fix
diff --git a/gdb/testsuite/gdb.base/readnever.exp b/gdb/testsuite/gdb.base/readnever.exp
index 737bc84..ab2e18e 100644
--- a/gdb/testsuite/gdb.base/readnever.exp
+++ b/gdb/testsuite/gdb.base/readnever.exp
@@ -20,6 +20,13 @@ if { [build_executable "failed to build" $testfile $srcfile { debug }] == -1 } {
     return -1
 }
 
+# See if we have target board readnow.exp or similar.
+if { [lsearch -exact $GDBFLAGS -readnow] != -1 \
+	 || [lsearch -exact $GDBFLAGS --readnow] != -1 } {
+    untested "--readnever not allowed in combination with --readnow"
+    return -1
+}
+
 save_vars { GDBFLAGS } {
     append GDBFLAGS " --readnever"
     clean_restart ${binfile}