RFR: JDK-8192876: MacOS build fails intermittently after JDK-8139653

[Erik Joelsson]

After my fix for linking with freetype, the build has started failing 
intermittently. This is caused by a closed library using the 
BUILD_LIBFONTMANAGER variable as prerequisite, but because of my change 
in JDK-8139653, this variable is no longer valid for that. In this fix, 
I restore BUILD_LIBFONTMANAGER to a valid prerequisite for libraries 
that need to link to it.

Bug: https://bugs.openjdk.java.net/browse/JDK-8192876
Webrev: http://cr.openjdk.java.net/~erikj/8192876/webrev.01/

/Erik