THRIFT-4582: Fix Xenial CI build issues (#1563)

* THRIFT-4582: fix xenial build issues

* THRIFT-2913: fix Thrift::ThreadPoolServer should serve inside a thread on xenial

* THRIFT-4478: Move Xenial up to dmd 2.075.1 as that is the new minimum
version that works since the changes for 2.080.0 went in.
diff --git a/.gitignore b/.gitignore
index be07a4e..3de1595 100644
--- a/.gitignore
+++ b/.gitignore
@@ -122,8 +122,9 @@
 /lib/cpp/test/OptionalRequiredTest
 /lib/cpp/test/SecurityTest
 /lib/cpp/test/SpecializationTest
-/lib/cpp/test/ReflectionTest
 /lib/cpp/test/RecursiveTest
+/lib/cpp/test/ReflectionTest
+/lib/cpp/test/RenderedDoubleConstantsTest
 /lib/cpp/test/TFDTransportTest
 /lib/cpp/test/TFileTransportTest
 /lib/cpp/test/TInterruptTest
@@ -241,6 +242,7 @@
 /lib/php/src/ext/thrift_protocol/build/
 /lib/php/src/ext/thrift_protocol/config.*
 /lib/php/src/ext/thrift_protocol/configure
+/lib/php/src/ext/thrift_protocol/configure.ac
 /lib/php/src/ext/thrift_protocol/configure.in
 /lib/php/src/ext/thrift_protocol/install-sh
 /lib/php/src/ext/thrift_protocol/libtool