[gdb/testsuite] Fix gdb.arch/amd64*.exp with local-remote-host-native.exp

There's a number of gdb.arch/amd64*.exp test-cases that fail with host+target
board local-remote-host-native.exp because of using a .S file, generated from
a .c file.

If a test-case compiles the .S file when executing on remote host,
the .S file is already copied from build to host, such that it's available for
the compiler.

But that's not the case for the .c file, which is needed by gdb to show a
source line:
...
(gdb) continue^M
Continuing.^M
^M
Breakpoint 2, fn2 (y=y@entry=25, x=x@entry=6) at amd64-entry-value-inline.c:32^M
32      in gdb.arch/amd64-entry-value-inline.c^M
(gdb) FAIL: gdb.arch/amd64-entry-value-inline.exp: continue to breakpoint: \
  break-here
...

Fix this by using "gdb_remote_download host <.c file>".

Tested on x86_64-linux, with host+target board local-remote-host-native.

gdb/testsuite/gdb.arch/amd64-entry-value-inline.exp

@@ -14,16 +14,21 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 set opts {}
-standard_testfile .S
+standard_testfile .S .c
 
 if [info exists COMPILE] {
     # make check RUNTESTFLAGS="gdb.arch/amd64-entry-value-inline.exp COMPILE=1"
-    standard_testfile
+    standard_testfile .c .c
     lappend opts debug optimize=-O2
 } else {
     require is_x86_64_m64_target
 }
 
+# Make .c available on the host.
+if [is_remote host] {
+    gdb_remote_download host $srcdir/$subdir/$srcfile2
+}
+
 if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} $opts] } {
     return -1
 }
@@ -32,8 +37,7 @@ if ![runto_main] {
     return -1
 }
 
-set srcfile $testfile.c
-gdb_breakpoint [gdb_get_line_number "break-here"]
+gdb_breakpoint [gdb_get_line_number "break-here" $srcfile2]
 
 gdb_continue_to_breakpoint "break-here" ".* break-here .*"
 gdb_test "p y" " = 25"

gdb/testsuite/gdb.arch/amd64-entry-value-param-dwarf5.exp

@@ -18,12 +18,17 @@ set opts {}
 
 if [info exists COMPILE] {
     # make check RUNTESTFLAGS="gdb.arch/amd64-entry-value-param-dwarf5.exp COMPILE=1"
-    set srcfile ${srcfile2}
+    standard_testfile .c .c
     lappend opts optimize=-O2 additional_flags=-gdwarf-5
 } else {
     require is_x86_64_m64_target
 }
 
+# Make .c available on the host.
+if [is_remote host] {
+    gdb_remote_download host $srcdir/$subdir/$srcfile2
+}
+
 if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} $opts] } {
     return -1
 }
@@ -32,8 +37,7 @@ if ![runto_main] {
     return -1
 }
 
-set srcfile $srcfile2
-gdb_breakpoint [gdb_get_line_number "break-here"]
+gdb_breakpoint [gdb_get_line_number "break-here" $srcfile2]
 
 with_test_prefix "call 1" {
     gdb_continue_to_breakpoint "break-here" ".* break-here .*"

gdb/testsuite/gdb.arch/amd64-entry-value-param.exp

@@ -18,12 +18,17 @@ set opts {}
 
 if [info exists COMPILE] {
     # make check RUNTESTFLAGS="gdb.arch/amd64-entry-value-param.exp COMPILE=1"
-    set srcfile ${srcfile2}
+    standard_testfile .c .c
     lappend opts debug optimize=-O2
 } else {
     require is_x86_64_m64_target
 }
 
+# Make .c available on the host.
+if [is_remote host] {
+    remote_download host $srcdir/$subdir/$srcfile2
+}
+
 if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} $opts] } {
     return -1
 }
@@ -32,8 +37,7 @@ if ![runto_main] {
     return -1
 }
 
-set srcfile $srcfile2
-gdb_breakpoint [gdb_get_line_number "break-here"]
+gdb_breakpoint [gdb_get_line_number "break-here" $srcfile2]
 
 with_test_prefix "call 1" {
     gdb_continue_to_breakpoint "break-here" ".* break-here .*"

gdb/testsuite/gdb.arch/amd64-entry-value-paramref.exp

@@ -17,6 +17,11 @@ standard_testfile .S .cc
 
 require is_x86_64_m64_target
 
+# Make .cc available on the host.
+if [is_remote host] {
+    gdb_remote_download host $srcdir/$subdir/$srcfile2
+}
+
 if { [prepare_for_testing_full "failed to prepare" \
 	  [list $testfile "c++" $srcfile {}]] } {
     return -1
@@ -26,8 +31,7 @@ if ![runto_main] {
     return -1
 }
 
-set srcfile $srcfile2
-gdb_breakpoint [gdb_get_line_number "break-here"]
+gdb_breakpoint [gdb_get_line_number "break-here" $srcfile2]
 
 gdb_continue_to_breakpoint "break-here" ".* break-here .*"
 gdb_test "frame" {bar \(ref=@0x[0-9a-f]+: 10, ref@entry=@0x[0-9a-f]+: <optimized out>\) at .*}

gdb/testsuite/gdb.arch/amd64-tailcall-ret.exp

@@ -14,16 +14,21 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 set opts {}
-standard_testfile .S
+standard_testfile .S .c
 
 if [info exists COMPILE] {
     # make check RUNTESTFLAGS="gdb.arch/amd64-tailcall-ret.exp COMPILE=1"
-    standard_testfile
+    standard_testfile .c .c
     lappend opts debug optimize=-O2
 } else {
     require is_x86_64_m64_target
 }
 
+# Make .c available on the host.
+if [is_remote host] {
+    gdb_remote_download host $srcdir/$subdir/$srcfile2
+}
+
 if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} $opts] } {
     return -1
 }