Fix several clang static analyzer dead store warnings.

* src/autofit/afhints.c (af_glyph_hints_reload,
af_glyph_hints_align_weak_points): Remove unnecessary assignments.

* src/bdf/bdflib.c (bdf_font_load): Ditto.

* src/pshinter/pshalgo.c (psh_glyph_compute_extrema,
psh_glyph_interpolate_other_points): Ditto.

* src/type1/t1load.c (T1_Set_MM_Blend): Ditto.
Minor fix for `make devel'.

* builds/freetype.mk (INCLUDE_FLAGS) [DEVEL_DIR]: Don't use
pkg-config for bzip2 since not all GNU/Linux distributions have
`bzip2.pc' (and the header file `bzlib.h' is located in /usr/include
normally).