let long path file test support long test root directory

See gpr-issues#213

testsuite/tests/long-windows-path/test.out

@@ -0,0 +1,6 @@
+Can't find ALI file for /main.adb
+
+Can't find ALI file for /dst/dir_name/src1/test1.ads
+
+Can't find ALI file for /dst/dir_name/src2/test2.ads
+

testsuite/tests/long-windows-path/test.py

@@ -0,0 +1,38 @@
+import os
+from e3.fs import mkdir, sync_tree
+from testsuite_support.builder_and_runner import BuilderAndRunner, GPRLS
+
+dest = 'dst'
+
+# return longest source file path if 'name' used as intermediate path
+def longest_path_length (name):
+    return len(os.getcwd() + '/' + dest + '/' + name + '/src1/test1.ads')
+
+dir_name = 'a'
+
+while longest_path_length (dir_name) < 255 :
+    dir_name = dir_name + 'a'
+
+src_path = os.path.join ('src_files')
+dest_path = os.path.join (dest, dir_name)
+
+mkdir(dest_path)
+sync_tree (src_path, dest_path)
+
+prj_gpr = open('prj.gpr', 'w')
+prj_gpr.write('with"' + dir_name + '/test1";project Prj is for Main use("main.adb");end Prj;')
+prj_gpr.close()
+
+test1_gpr = open(os.path.join (dest, dir_name, 'test1.gpr'), 'w')
+test1_gpr.write('with"' + dir_name + '/test2";project Test1 is for Source_Dirs use("src1");end Test1;')
+test1_gpr.close()
+
+p = BuilderAndRunner().run(
+    [GPRLS, "-U", "-P", "prj.gpr"],
+    env={"GPR_PROJECT_PATH": os.getcwd() + '/' + dest},
+    output='gprls.out',
+)
+
+for line in open('gprls.out'):
+    print(line.replace(dir_name,'dir_name'))
+

testsuite/tests/long-windows-path/test.yaml

@@ -0,0 +1,4 @@
+description: let a long relative path be imported from a 255 chars absolute path
+driver: python_script
+control:
+- [SKIP, "True", "uses gprls that is not built from gpr2-next"]