nvtool: fix compiler flag settings This makes the build respect CPPFLAGS and LDFLAGS correctly. It also drops the hardcoded -L path to the host system's libraries. BUG=None TEST=`emerge-x86-alex tpm` still works and uses right flags Change-Id: I86f2904dc3975ffce18aa456e5adbb92a886c375 Reviewed-on: https://gerrit.chromium.org/gerrit/60836 Reviewed-by: Luigi Semenzato <[email protected]> Commit-Queue: Mike Frysinger <[email protected]> Tested-by: Mike Frysinger <[email protected]>