[gdb/symtab] Add symbol with inherited DW_AT_const_value to psymtabs

Consider the test-case added in this patch, with resulting dwarf (related to
variable aaa):
...
 <0><d2>: Abbrev Number: 2 (DW_TAG_partial_unit)
 <1><eb>: Abbrev Number: 4 (DW_TAG_variable)
    <ec>   DW_AT_name        : aaa
    <f0>   DW_AT_type        : <0xe4>
    <f4>   DW_AT_const_value : 1
 <0><10c>: Abbrev Number: 2 (DW_TAG_compile_unit)
    <10e>   DW_AT_name        : <artificial>
 <1><11b>: Abbrev Number: 3 (DW_TAG_variable)
    <11c>   DW_AT_abstract_origin: <0xeb>
...

When running the test-case, we see:
...
(gdb) p aaa^M
No symbol "aaa" in current context.^M
(gdb) FAIL: gdb.dwarf2/imported-unit-abstract-const-value.exp: p aaa
...
while with target board readnow.exp, we have:
...
(gdb) p aaa^M
$1 = 1^M
...

This is due to the fact that there's no aaa symbol in the partial symtabs:
...
Partial symtab for source file <artificial>@0x101 (object 0x351cf40)^M
   ...
Global partial symbols:^M
    `main', function, 0x4004a7^M
^M
...
which is due to the fact that when attempting to add the symbol corresponding
to DIE 0x11b in add_partial_symbol:
...
(gdb) p /x pdi->sect_off
$4 = 0x11b
(gdb) p pdi.has_const_value
$5 = 0
...
it seems the DW_AT_const_value was not inherited from DIE 0xeb, and
consequently we leave without adding a partial symbol.

Fix this by making sure that partial_die_info::has_const_value is inherited
in partial_die_info::fixup.

Build and reg-tested on x86_64-linux.

Tested test-case with target boards readnow, cc-with-gdb-index and
cc-with-debug-names.  The "print aaa" test fails for cc-with-gdb-index, that's
PR25791, the test passes when applying the corresponding proposed patch.

gdb/ChangeLog:

2020-04-07  Tom de Vries  <tdevries@suse.de>

	PR symtab/25796
	* dwarf2/read.c (can_have_DW_AT_const_value_p): New function.
	(partial_die_info::fixup): Inherit has_const_value.

gdb/testsuite/ChangeLog:

2020-04-07  Tom de Vries  <tdevries@suse.de>

	PR symtab/25796
	* gdb.dwarf2/imported-unit-abstract-const-value.exp: New file.

1 files changed, 98 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/imported-unit-abstract-const-value.exp b/gdb/testsuite/gdb.dwarf2/imported-unit-abstract-const-value.exp
new file mode 100644
index 00000000000..f93dc123885
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/imported-unit-abstract-const-value.exp
@@ -0,0 +1,98 @@
+# Copyright 2020 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/>.
+
+# Test that a concrete var importing an abstract var using
+# DW_AT_abstract_origin inherits the DW_AT_const_value attribute.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+    return 0
+};
+
+standard_testfile main.c .S
+
+set executable ${testfile}
+set asm_file [standard_output_file ${srcfile2}]
+
+# We need to know the size of integer type in order
+# to write some of the debugging info we'd like to generate.
+if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] {
+    return -1
+}
+
+# Create the DWARF.
+Dwarf::assemble $asm_file {
+    declare_labels cu_label main_label int_label
+    declare_labels aaa_label
+    set int_size [get_sizeof "int" 4]
+
+    global srcdir subdir srcfile
+
+    extern main
+
+    set main_range [function_range main ${srcdir}/${subdir}/${srcfile}]
+    set main_start [lindex $main_range 0]
+    set main_length [lindex $main_range 1]
+
+    cu {} {
+	cu_label: partial_unit {
+	    {language @DW_LANG_C}
+	    {name "imported_unit.c"}
+	} {
+	    int_label: base_type {
+		{byte_size $int_size sdata}
+		{encoding @DW_ATE_signed}
+		{name int}
+	    }
+
+	    aaa_label: DW_TAG_variable {
+		{name aaa}
+		{type :$int_label}
+		{const_value 1 DW_FORM_sdata}
+	    }
+
+	    main_label: subprogram {
+		{name main}
+		{type :$int_label}
+		{external 1 flag}
+	    }
+	}
+    }
+
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    DW_TAG_variable {
+		{abstract_origin %$aaa_label}
+	    }
+	    subprogram {
+		{abstract_origin %$main_label}
+		{low_pc $main_start addr}
+		{high_pc "$main_start + $main_length" addr}
+	    }
+	}
+    }
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+gdb_test "p aaa" "= 1"