[gdb/testsuite] Add gdb.dwarf2/imported-unit-c.exp

This test-case is intended to excercise this code in process_imported_unit_die:
...
      /* We're importing a C++ compilation unit with tag DW_TAG_compile_unit
	 into another compilation unit, at root level.  Regard this as a hint,
	 and ignore it.  */
      if (die->parent && die->parent->parent == NULL
	  && per_cu->unit_type == DW_UT_compile
	  && per_cu->lang == language_cplus)
	return;
...
in the sense that the test-case should fail if the
"per_cu->lang == language_cplus" clause is removed.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2021-06-22  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/imported-unit-c.exp: New file.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2021-06-22  Tom de Vries  <tdevries@suse.de>
+
+	* gdb.dwarf2/imported-unit-c.exp: New file.
+
 2021-06-22  Andrew Burgess  <andrew.burgess@embecosm.com>
 
 	* gdb.server/server-kill.exp: Introduce global kill_pid_of, and

gdb/testsuite/gdb.dwarf2/imported-unit-c.exp

@@ -0,0 +1,110 @@
+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-foo.c .S
+
+set executable ${testfile}
+set asm_file [standard_output_file ${srcfile2}]
+
+# We need to know the size of integer and address types in order
+# to write some of the debugging info we'd like to generate.
+if [prepare_for_testing "failed to prepare" ${testfile} ${srcfile} {debug}] {
+    return -1
+}
+
+# Create the DWARF.
+Dwarf::assemble $asm_file {
+    declare_labels cu_label cu2_label int_label int2_label
+    set int_size [get_sizeof "int" 4]
+
+    # imported CU 1: inty unsigned
+    cu {} {
+	cu_label: compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    int_label: base_type {
+		{byte_size $int_size sdata}
+		{encoding @DW_ATE_unsigned}
+		{name {unsigned int}}
+	    }
+            DW_TAG_typedef {
+                {DW_AT_name inty}
+                {DW_AT_type :$int_label}
+            }
+	}
+    }
+
+    # imported CU 2: inty signed
+    cu {} {
+	cu2_label: compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    int2_label: base_type {
+		{byte_size $int_size sdata}
+		{encoding @DW_ATE_signed}
+		{name {int}}
+	    }
+            DW_TAG_typedef {
+                {DW_AT_name inty}
+                {DW_AT_type :$int2_label}
+            }
+	}
+    }
+
+    # main CU
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    imported_unit {
+		{import %$cu2_label}
+	    }
+
+	    subprogram {
+		{MACRO_AT_func {main}}
+		{external 1 flag}
+	    }
+	}
+    }
+
+    # foo CU
+    cu {} {
+	compile_unit {
+	    {language @DW_LANG_C}
+	    {name "<artificial>"}
+	} {
+	    imported_unit {
+		{import %$cu_label}
+	    }
+
+	    subprogram {
+		{MACRO_AT_func {foo}}
+		{external 1 flag}
+	    }
+	}
+    }
+
+}
+
+if { [prepare_for_testing "failed to prepare" ${testfile} \
+	  [list $srcfile $asm_file] {nodebug}] } {
+    return -1
+}
+
+if ![runto_main] {
+    return -1
+}
+
+gdb_test "ptype inty" "type = int" "ptype in main"
+
+gdb_breakpoint "foo"
+gdb_continue_to_breakpoint "continue to breakpoint for foo"
+
+gdb_test "ptype inty" "type = unsigned int" "ptype in foo"