For starters it was cloning PATH when LD_LIBRARY_PATH would be more
appropriate.
More importantly it isn't needed most of the time. Indeed I'm usually
unsetting it whenever I build stuff so that the run path doesn't leak
into compiled code.
Set it manually as and when appropriate.
C_INCLUDE_PATH:incdirs
CPLUS_INCLUDE_PATH:@C_INCLUDE_PATH
LD_LIBRARY_PATH:libdirs
-LD_RUN_PATH:@PATH
MANPATH:mandirs
PKG_CONFIG_PATH:pkgdirs
"