[libcalamares] Reduce warnings with Clang 9 (Boost::Python)

- The boost headers fall foul of tons of Clang warnings, so introduce
   a mechanism like moc-headers for turning off most of those warnings.

src/libcalamares/PythonHelper.cpp

@@ -26,8 +26,13 @@
 #include <QFileInfo>
 
 #undef slots
+#include "utils/boost-warnings.h"
 #include <boost/python.hpp>
 
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 namespace bp = boost::python;
 
 namespace CalamaresPython

src/libcalamares/PythonHelper.h

@@ -25,10 +25,16 @@
 #include <QStringList>
 
 #undef slots
+#include "utils/boost-warnings.h"
+
 #include <boost/python/dict.hpp>
 #include <boost/python/list.hpp>
 #include <boost/python/object.hpp>
 
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 namespace CalamaresPython
 {
 

src/libcalamares/PythonJobApi.cpp

@@ -32,8 +32,13 @@
 #include <QStandardPaths>
 
 #undef slots
+#include "utils/boost-warnings.h"
 #include <boost/python.hpp>
 
+#ifdef __clang__
+#pragma clang diagnostic pop
+#endif
+
 namespace bp = boost::python;
 
 static int

src/libcalamares/utils/boost-warnings.h

@@ -0,0 +1,8 @@
+#ifdef __clang__
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wreserved-id-macro"
+#pragma clang diagnostic ignored "-Wold-style-cast"
+#pragma clang diagnostic ignored "-Wzero-as-null-pointer-constant"
+#pragma clang diagnostic ignored "-Wextra-semi-stmt"
+#pragma clang diagnostic ignored "-Wall"
+#endif