build: only set libpath if one is reported by apr-1-config
build: only set libpath if one is reported by apr-1-config

reported to break in CentOS 4.x when using a Fedora apr1 package by Bernard


torkelsson/monitor-core,mjzhou/monitor-core,dmourati/monitor-core,lawrencewu/monitor-core,lawrencewu/monitor-core,mjzhou/monitor-core,torkelsson/monitor-core,torkelsson/monitor-core,lawrencewu/monitor-core,mjzhou/monitor-core,torkelsson/monitor-core,phreakocious/monitor-core,torkelsson/monitor-core,phreakocious/monitor-core,hinesmr/monitor-core,NoodlesNZ/monitor-core,ganglia/monitor-core,ganglia/monitor-core,NoodlesNZ/monitor-core,sdgdsffdsfff/monitor-core,mjzhou/monitor-core,torkelsson/monitor-core,NoodlesNZ/monitor-core,ganglia/monitor-core,mjzhou/monitor-core,fastly/monitor-core,dmourati/monitor-core,fastly/monitor-core,hinesmr/monitor-core,dmourati/monitor-core,ganglia/monitor-core,dmourati/monitor-core,hinesmr/monitor-core,sdgdsffdsfff/monitor-core,sdgdsffdsfff/monitor-core,phreakocious/monitor-core,mjzhou/monitor-core,lawrencewu/monitor-core,hinesmr/monitor-core,fastly/monitor-core,dmourati/monitor-core,lawrencewu/monitor-core,phreakocious/monitor-core,ganglia/monitor-core,NoodlesNZ/monitor-core,NoodlesNZ/monitor-core,fastly/monitor-core,phreakocious/monitor-core,sdgdsffdsfff/monitor-core,dmourati/monitor-core,sdgdsffdsfff/monitor-core,ganglia/monitor-core,fastly/monitor-core,mjzhou/monitor-core,NoodlesNZ/monitor-core,fastly/monitor-core,ganglia/monitor-core,phreakocious/monitor-core,sdgdsffdsfff/monitor-core,fastly/monitor-core,lawrencewu/monitor-core,hinesmr/monitor-core,sdgdsffdsfff/monitor-core,lawrencewu/monitor-core,ganglia/monitor-core,torkelsson/monitor-core,NoodlesNZ/monitor-core,phreakocious/monitor-core