Make test-all and test-spec runnable on Android

Calling some syscall functions such as Dir.chroot causes SIGSYS instead
of EPERM on Android.
This change skips all tests that stops the test-suite run.

spec/ruby/core/dir/chroot_spec.rb

@@ -9,7 +9,7 @@ platform_is_not :windows do
     end
   end
 
-  platform_is_not :cygwin do
+  platform_is_not :cygwin, :android do
     as_user do
       describe "Dir.chroot as regular user" do
         before :all do

spec/ruby/core/process/groups_spec.rb

@@ -14,7 +14,7 @@ describe "Process.groups" do
 end
 
 describe "Process.groups=" do
-  platform_is_not :windows do
+  platform_is_not :windows, :android do
     as_superuser do
       it "sets the list of gids of groups in the supplemental group access list" do
         groups = Process.groups

spec/ruby/core/process/initgroups_spec.rb

@@ -1,7 +1,7 @@
 require_relative '../../spec_helper'
 
 describe "Process.initgroups" do
-  platform_is_not :windows do
+  platform_is_not :windows, :android do
     as_user do
       it "initializes the supplemental group access list" do
         name = `id -un`.strip

test/fiddle/helper.rb

@@ -10,6 +10,13 @@ case RUBY_PLATFORM
 when /cygwin/
   libc_so = "cygwin1.dll"
   libm_so = "cygwin1.dll"
+when /android/
+  libdir = '/system/lib'
+  if [0].pack('L!').size == 8
+    libdir = '/system/lib64'
+  end
+  libc_so = File.join(libdir, "libc.so")
+  libm_so = File.join(libdir, "libm.so")
 when /linux/
   libdir = '/lib'
   case [0].pack('L!').size

test/pathname/test_pathname.rb

@@ -789,6 +789,7 @@ class TestPathname < Test::Unit::TestCase
   end
 
   def test_birthtime
+    skip if RUBY_PLATFORM =~ /android/
     # Check under a (probably) local filesystem.
     # Remote filesystems often may not support birthtime.
     with_tmpchdir('rubytest-pathname') do |dir|

test/ruby/test_dir.rb

@@ -122,6 +122,7 @@ class TestDir < Test::Unit::TestCase
   end
 
   def test_chroot_nodir
+    skip if RUBY_PLATFORM =~ /android/
     assert_raise(NotImplementedError, Errno::ENOENT, Errno::EPERM
 		) { Dir.chroot(File.join(@nodir, "")) }
   end

test/ruby/test_file_exhaustive.rb

@@ -642,6 +642,7 @@ class TestFileExhaustive < Test::Unit::TestCase
   end
 
   def test_birthtime
+    skip if RUBY_PLATFORM =~ /android/
     [regular_file, utf8_file].each do |file|
       t1 = File.birthtime(file)
       t2 = File.open(file) {|f| f.birthtime}

test/ruby/test_process.rb

@@ -1583,6 +1583,7 @@ class TestProcess < Test::Unit::TestCase
   end
 
   def test_setegid
+    skip "root can use Process.egid on Android platform" if RUBY_PLATFORM =~ /android/
     assert_nothing_raised(TypeError) {Process.egid += 0}
   rescue NotImplementedError
   end
@@ -1871,6 +1872,7 @@ class TestProcess < Test::Unit::TestCase
   end
 
   def test_execopts_uid
+    skip "root can use uid option of Kernel#system on Android platform" if RUBY_PLATFORM =~ /android/
     feature6975 = '[ruby-core:47414]'
 
     [30000, [Process.uid, ENV["USER"]]].each do |uid, user|
@@ -1902,6 +1904,7 @@ class TestProcess < Test::Unit::TestCase
 
   def test_execopts_gid
     skip "Process.groups not implemented on Windows platform" if windows?
+    skip "root can use Process.groups on Android platform" if RUBY_PLATFORM =~ /android/
     feature6975 = '[ruby-core:47414]'
 
     groups = Process.groups.map do |g|