Add missing Pango symbols

Currently Pango functions are hidden behind linux and not compiled
in as part of the build. Not all JavaFX applications are affected by
this, but applications that do advanced text layout that require Pango
internally cause an UnsatisfiedLinkError at runtime.

Caused by: java.lang.UnsatisfiedLinkError: com.sun.javafx.font.freetype.OSPango.pango_ft2_font_map_new()J
at com.sun.javafx.font.freetype.OSPango.pango_ft2_font_map_new(Native Method)
at com.sun.javafx.font.freetype.PangoGlyphLayout.layout(PangoGlyphLayout.java:88)
at com.sun.javafx.text.PrismTextLayout.shape(PrismTextLayout.java:834)
at com.sun.javafx.text.PrismTextLayout.layout(PrismTextLayout.java:1064)
at com.sun.javafx.text.PrismTextLayout.ensureLayout(PrismTextLayout.java:223)
...

PR: 220566
Submitted by: Stefan Ehmann <shoesoft@gmx.net>
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D11545
MFH: 2017Q3