[committed][gdb/testsuite] Fix testing build_executable result

[Tom de Vries]

Hi,

When running with target board unix/-feliminate-dwarf2-dups, we run into these
FAILs:
...
FAIL: gdb.cp/rvalue-ref-params.exp: print value of f1 on Child&& in f2
FAIL: gdb.cp/ref-params.exp: print value of f1 on Child in main
FAIL: gdb.cp/ref-params.exp: print value of f2 on Child in main
FAIL: gdb.cp/ref-params.exp: print value of f1 on Child& in f2
FAIL: gdb.cp/ref-params.exp: print mf1(MQ)
FAIL: gdb.cp/ref-params.exp: print mf2(MQ)
FAIL: gdb.cp/ref-params.exp: print f1(MQR)
FAIL: gdb.cp/ref-params.exp: print mf1(MQR)
FAIL: gdb.cp/ref-params.exp: print mf2(MQR)
...

This is due to comparing the result of build_executable to 1, while
build_executable returns either 0 for success, or -1 for failure.

Fix this by comparing with -1 instead.

Tested on x86_64-linux.

Committed to trunk.

Thanks,
- Tom

[gdb/testsuite] Fix testing build_executable result

gdb/testsuite/ChangeLog:

2020-03-07  Tom de Vries  <tdevries@suse.de>

	* gdb.cp/ref-params.exp: Compare build_executable result with -1.
	* gdb.cp/rvalue-ref-params.exp: Same.

---
 gdb/testsuite/gdb.cp/ref-params.exp        | 2 +-
 gdb/testsuite/gdb.cp/rvalue-ref-params.exp | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/gdb/testsuite/gdb.cp/ref-params.exp b/gdb/testsuite/gdb.cp/ref-params.exp
index 2b45ee7fc8..2b00501706 100644
--- a/gdb/testsuite/gdb.cp/ref-params.exp
+++ b/gdb/testsuite/gdb.cp/ref-params.exp
@@ -24,7 +24,7 @@ if { [skip_cplus_tests] } { continue }
 
 standard_testfile .cc
 
-if {[build_executable $testfile.exp $testfile $srcfile {debug c++}] == 1} {
+if {[build_executable $testfile.exp $testfile $srcfile {debug c++}] == -1} {
     return -1
 }
 
diff --git a/gdb/testsuite/gdb.cp/rvalue-ref-params.exp b/gdb/testsuite/gdb.cp/rvalue-ref-params.exp
index e1c54aa40a..fec4b6fadd 100644
--- a/gdb/testsuite/gdb.cp/rvalue-ref-params.exp
+++ b/gdb/testsuite/gdb.cp/rvalue-ref-params.exp
@@ -21,7 +21,7 @@ if {[skip_cplus_tests]} { continue }
 standard_testfile .cc
 
 if {[prepare_for_testing $testfile.exp $testfile $srcfile \
-    {debug c++ additional_flags="-std=gnu++11"}] == 1} {
+    {debug c++ additional_flags="-std=gnu++11"}] == -1} {
     return -1
 }