editors/libreoffice: fix build on GCC architectures

GCC architectures have /usr/bin/gperf binary resulting in failing to configure:
checking for gperf... /usr/bin/gperf
checking whether gperf is new enough... configure: error: "GNU gperf 3.0.3" is too old or unrecognized, must be at least gperf 3.1

Put back GPERF to CONFIGURE_ENV to fix the build.

PR: 243215
Approved by: lwhsu (maintainer)