[gdb/testsuite] Compile ada with -lgnarl_pic and -lgnat_pic if required

On openSUSE Leap 15.1, when running the gdb.ada testsuite with target board
unix/-fPIE/-pie, I get:
...
nr of unexpected failures        158
...

The problem is that although due to commit abcf2cc85a3 "[gdb/testsuite] Fix
ada tests with -fPIE/-pie" we try to compile say, hello.adb like so:
...
$ gnatmake -fPIE -largs -pie -margs hello.adb
...
this is not sufficient, because gnatlink is try to link in libgnat.a, which is
not Position Independent Code.

This issue has been filed as gcc PR ada/87936 - "gnatlink fails with -pie".

Work around this issue by compiling with _pic versions of lgnarl and lgnat:
...
$ gnatmake -fPIE -largs -pie -lgnarl_pic -lgnat_pic -margs hello.adb
...
if that is required to make hello.adb compile.

Using this patch, I get instead:
...
nr of unexpected failures        2
...
where one failure also happens with native, and the other has been filed as
gdb PR24890.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2019-10-10  Tom de Vries  <tdevries@suse.de>

	PR testsuite/24888
	* lib/ada.exp (gdb_simple_compile_ada): New proc.
	(calculating_ada_needs_libs_pic_suffix): New global, initialized to 0.
	(gdb_ada_needs_libs_pic_suffix): New caching proc.
	(target_compile_ada_from_dir): Append -largs -lgnarl_pic -lgnat_pic
	-margs to multilib_flags if required.
	(gdb_compile_ada_1): Factor out of ...
	(gdb_compile_ada): ... here.

---
 gdb/testsuite/lib/ada.exp | 86 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 85 insertions(+), 1 deletion(-)

diff --git a/gdb/testsuite/lib/ada.exp b/gdb/testsuite/lib/ada.exp
index 45c41806a64..4bdb12051ec 100644
--- a/gdb/testsuite/lib/ada.exp
+++ b/gdb/testsuite/lib/ada.exp
@@ -17,6 +17,78 @@
 # after having temporarily changed the current working directory to
 # BUILDDIR.
 
+proc gdb_simple_compile_ada {name code {type object} {compile_flags {}} {object obj}} {
+    upvar $object obj
+
+    switch -regexp -- $type {
+        "executable" {
+            set postfix "x"
+        }
+        "object" {
+            set postfix "o"
+        }
+        "preprocess" {
+            set postfix "i"
+        }
+        "assembly" {
+            set postfix "s"
+        }
+    }
+    set src [standard_temp_file $name.adb]
+    set obj [standard_temp_file $name-[pid].$postfix]
+    set compile_flags [concat $compile_flags {debug nowarnings quiet}]
+
+    gdb_produce_source $src $code
+
+    verbose "$name:  compiling testfile $src" 2
+    set lines [gdb_compile_ada_1 $src $obj $type $compile_flags]
+
+    if ![string match "" $lines] then {
+        verbose "$name:  compilation failed, returning 0" 2
+        return 0
+    }
+    return 1
+}
+
+global calculating_ada_needs_libs_pic_suffix
+set calculating_ada_needs_libs_pic_suffix 0
+gdb_caching_proc gdb_ada_needs_libs_pic_suffix {
+    global calculating_ada_needs_libs_pic_suffix
+    if { $calculating_ada_needs_libs_pic_suffix } {
+	return 0
+    }
+    set ada_hello {
+	with Ada.Text_IO;
+
+	procedure Hello is
+	begin
+	Ada.Text_IO.Put_Line("Hello, world!");
+	end Hello;
+    }
+
+    set calculating_ada_needs_libs_pic_suffix 1
+    set res \
+	[gdb_simple_compile_ada hello $ada_hello executable]
+    if { $res == 1 } {
+	set calculating_ada_needs_libs_pic_suffix 0
+	return 0
+    }
+    set flags {}
+    lappend flags "additional_flags=-largs"
+    lappend flags "additional_flags=-lgnarl_pic"
+    lappend flags "additional_flags=-lgnat_pic"
+    lappend flags "additional_flags=-margs"
+    set res \
+	[gdb_simple_compile_ada hello $ada_hello executable $flags]
+    if { $res == 1 } {
+	set calculating_ada_needs_libs_pic_suffix 0
+	return 1
+    }
+
+    set calculating_ada_needs_libs_pic_suffix 0
+    return 0
+}
+
 proc target_compile_ada_from_dir {builddir source dest type options} {
     set saved_cwd [pwd]
 
@@ -29,6 +101,10 @@ proc target_compile_ada_from_dir {builddir source dest type options} {
 	    # Pretend gnatmake supports -pie/-no-pie, route it to
 	    # linker.
 	    append multilib_flag " -largs $op -margs"
+	    if { $op == "-pie" && [gdb_ada_needs_libs_pic_suffix]} {
+		# Work around PR gcc/87936 by using libgnat_pic
+		append multilib_flag " -largs -lgnarl_pic -lgnat_pic -margs"
+	    }
 	} else {
 	    append multilib_flag " $op"
 	}
@@ -54,7 +130,7 @@ proc target_compile_ada_from_dir {builddir source dest type options} {
 
 # Compile some Ada code.
 
-proc gdb_compile_ada {source dest type options} {
+proc gdb_compile_ada_1 {source dest type options} {
 
     set srcdir [file dirname $source]
     set gprdir [file dirname $srcdir]
@@ -78,6 +154,14 @@ proc gdb_compile_ada {source dest type options} {
     # We therefore simply check whether the dest file has been created
     # or not. Unless not present, the build has succeeded.
     if [file exists $dest] { set result "" }
+    return $result
+}
+
+# Compile some Ada code.
+
+proc gdb_compile_ada {source dest type options} {
+    set result [gdb_compile_ada_1 $source $dest $type $options]
+
     gdb_compile_test $source $result
     return $result
 }