[gdb/testsuite] Add gdb.base/include-main.exp

The test-case gdb.ada/dgopt.exp uses the -gnatD switch, in combination with
-gnatG.

This causes the source file $src/gdb/testsuite/gdb.ada/dgopt/x.adb to be
expanded into $build/gdb/testsuite/outputs/gdb.ada/dgopt/x.adb.dg, and the
debug information should refer to the x.adb.dg file.

That is the case for the .debug_line part:
...
The Directory Table is empty.

 The File Name Table (offset 0x1c):
  Entry Dir     Time    Size    Name
  1     0       0       0       x.adb.dg
...
but not for the .debug_info part:
...
    <11>   DW_AT_name        : $src/gdb/testsuite/gdb.ada/dgopt/x.adb
    <15>   DW_AT_comp_dir    : $build/gdb/testsuite/outputs/gdb.ada/dgopt
...

Filed as PR gcc/103436.

In C we can generate similar debug information, using a source file that does
not contain any code, but includes another one that does:
...
 $ cat gdb/testsuite/gdb.base/include-main.c
 #include "main.c"
...
such that in the .debug_line part we have:
...
 The Directory Table (offset 0x1c):
  1     /home/vries/gdb_versions/devel/src/gdb/testsuite/gdb.base

 The File Name Table (offset 0x57):
  Entry Dir     Time    Size    Name
  1     1       0       0       main.c
...
and in the .debug_info part:
...
    <11>   DW_AT_name        : $src/gdb/testsuite/gdb.base/include-main.c
    <15>   DW_AT_comp_dir    : $build/gdb/testsuite
...

Add a C test-case that mimics gdb.ada/dgopt.exp, that is:
- generate debug info as described above,
- issue a list of a line in include-main.c, while the corresponding
  CU is not expanded yet.

Tested on x86_64-linux.

gdb/testsuite/gdb.base/include-main.c

@@ -0,0 +1,18 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2021 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#include "main.c"

gdb/testsuite/gdb.base/include-main.exp

@@ -0,0 +1,47 @@
+# Copyright 2021 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# C test-case that mimics gdb.ada/dgopt.exp.
+
+standard_testfile .c main.c
+
+if { [build_executable "failed to prepare" $testfile $srcfile {debug}] } {
+    return -1
+}
+
+clean_restart
+
+# Set language explicitly, to avoid expanding the include-main.c CU for the
+# language lookup (this is currently not required, but may be after
+# integration of the no-more-psym branch).
+# This to make sure that the source file lookup we do later triggers the
+# symtab expansion.
+gdb_test_no_output "set language c"
+
+gdb_load $binfile
+
+# Verify that no CU was expanded.
+gdb_test_no_output "maint info symtab"
+
+# List a line in include-main.c.  The tricky bit is that there's no code in
+# include-main.c, so the file should not occur in the .debug_line info.
+# GDB needs to find the file based on the CU's DW_AT_name/DW_AT_comp_dir.
+set line [gdb_get_line_number "include" $srcfile]
+gdb_test "list $srcfile:$line" "$line\[ \t\]*#include \"main.c\""
+
+# For completeness, also try to list a line in the file that does contain
+# code.
+set line [gdb_get_line_number "main" $srcfile2]
+gdb_test "list $srcfile2:$line" "$line\[ \t\]*main \\(void\\)\r\n.*"

gdb/testsuite/gdb.base/main.c

@@ -0,0 +1,22 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2021 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+int
+main (void)
+{
+  return 0;
+}