fix Win32 compile failure in r883540, reported by Gregg Smith

DEFAULT_REL_RUNTIMEDIR defined only in mpm_default.h for 
NetWare and dsp-based Win32 builds

mpm_default.h not in normal include path on Unix

thus, hardcode "logs" directory when DEFAULT_REL_RUNTIMEDIR
isn't defined

(file-based mutexes aren't configurable for those platforms anyway)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@883828 13f79535-47bb-0310-9956-ffa450edef68