[PATCH 3/7] gdb/testsuite: Let gdb_simple_compile take empty default flags

I noticed this while renaming nodebug to symtab.

gdb_simple_compile and its wrapper gdb_can_simple_compile take a
default_compile_flags argument that, when left unspecified, defaults
to a debug build ("debug nowarnings quiet").  The check for
"unspecified argument" is:

    if { $default_compile_flags == "" } {

which makes the default indistinguishable from a caller explicitly
passing "", so there was no way to ask for a build with no default
flags at all -- passing an empty list still gets you the default
flags.

Fix this by using a distinct "DEFAULT" sentinel for the unspecified
case instead.

Note no caller passes an explicit empty default_compile_flags today.

Change-Id: I30235fa1d28eb93dfdf08248af26669a7336d708
---
 gdb/testsuite/lib/gdb.exp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index d34ac30f2f0..b268152bdb7 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -6293,7 +6293,7 @@ gdb_caching_proc universal_compile_options_assembly {} {
 # Return 1 if code can be compiled
 # Leave the file name of the resulting object in the upvar object.
 
-proc gdb_simple_compile {name code {type object} {compile_flags {}} {object obj} {default_compile_flags {}}} {
+proc gdb_simple_compile {name code {type object} {compile_flags {}} {object obj} {default_compile_flags DEFAULT}} {
     upvar $object obj
 
     switch -regexp -- $type {
@@ -6331,7 +6331,7 @@ proc gdb_simple_compile {name code {type object} {compile_flags {}} {object obj}
     }
     set src [standard_temp_file $name.$ext]
     set obj [standard_temp_file $name.$postfix]
-    if { $default_compile_flags == "" } {
+    if { $default_compile_flags eq "DEFAULT" } {
 	set compile_flags [concat $compile_flags {debug nowarnings quiet}]
     } else {
 	set compile_flags [concat $compile_flags $default_compile_flags]
@@ -6357,7 +6357,7 @@ proc gdb_simple_compile {name code {type object} {compile_flags {}} {object obj}
 # Return 1 if code can be compiled
 # Delete all created files and objects.
 
-proc gdb_can_simple_compile {name code {type object} {compile_flags ""} {default_compile_flags ""}} {
+proc gdb_can_simple_compile {name code {type object} {compile_flags ""} {default_compile_flags DEFAULT}} {
     set ret [gdb_simple_compile $name $code $type $compile_flags temp_obj \
 		 $default_compile_flags]
     file delete $temp_obj
-- 
2.54.0