GL: don't use std::pair in Context internals.

And this, this change allows the growable Array to use malloc() instead
of new, and thus also realloc(), saving unnecessary reallocations if the
memory can be grown in-place. All because Containers::Pair is trivially
copyable while std::pair wasn't.

There isn't any good reason to use the STL anymore.

src/Magnum/GL/Context.cpp

@@ -994,7 +994,7 @@ bool Context::tryCreate(const Configuration& configuration) {
     if(!_driverWorkarounds.isEmpty()) {
         Debug{output} << "Using driver workarounds:";
         for(const auto& workaround: _driverWorkarounds)
-            if(!workaround.second) Debug(output) << "   " << workaround.first;
+            if(!workaround.second()) Debug(output) << "   " << workaround.first();
     }
 
     /* Fetch default framebuffer size and set up default clear color. If we are

src/Magnum/GL/Context.h

@@ -915,7 +915,7 @@ class MAGNUM_GL_EXPORT Context {
             then can be discarded -- what to do? we could avoid including
             Array altogether */
         /* True means known and disabled, false means known */
-        Containers::Array<std::pair<Containers::StringView, bool>> _driverWorkarounds;
+        Containers::Array<Containers::Pair<Containers::StringView, bool>> _driverWorkarounds;
         Containers::Array<Extension> _disabledExtensions;
         Implementation::ContextConfigurationFlags _configurationFlags;
 };

src/Magnum/GL/Implementation/driverSpecific.cpp

@@ -24,6 +24,7 @@
 */
 
 #include <Corrade/Containers/GrowableArray.h>
+#include <Corrade/Containers/Pair.h>
 #include <Corrade/Containers/StringView.h>
 #include <Corrade/Containers/StringIterable.h>
 
@@ -612,7 +613,7 @@ bool Context::isDriverWorkaroundDisabled(const Containers::StringView workaround
        compare just data pointers instead of the whole string as we store only
        the views in the KnownWorkarounds list. */
     for(const auto& i: _driverWorkarounds)
-        if(i.first.data() == found.data()) return i.second;
+        if(i.first().data() == found.data()) return i.second();
     arrayAppend(_driverWorkarounds, InPlaceInit, found, false);
     return false;
 }