[cmake] freetype2.pc cannot request (Requires.private) bzip2

Migrated from: [SAVANNAH-56073]

Anonymous reported:

Using cmake and freetype 2.10.0 generates the file:

freetype2.pc:
-----------------------
prefix=/usr/local
exec_prefix=${prefix}
libdir=${prefix}/lib
includedir=${prefix}/include

Name: FreeType 2
URL: https://freetype.org
Description: A free, high-quality, and portable font engine.
Version: 2.10.0
Requires:
Requires.private: zlib, bzip2, libpng, harfbuzz
Libs: -L${libdir} -lfreetype
Libs.private:
Cflags: -I${includedir}/freetype2
-----------------------

Since libbzip2 does not install bzip2.pc, freetype2.pc cannot request that file.