cfg: shell host triple x86_64-unknown-linux-gnu

cfg: host for x86_64-unknown-linux-gnu is x86_64
cfg: unix-y environment
cfg: using gcc
cfg: no pdflatex found, omitting doc/rust.pdf
cfg: no llnextgen found, omitting grammar-verification
cfg: including install rules
install: /usr/local/bin/rustc fix to address rust-lang#2555

mk/install.mk

@@ -58,7 +58,7 @@ install: all install-host install-targets
 
 # Shorthand for build/stageN/bin
 HB = $(HBIN$(ISTAGE)_H_$(CFG_HOST_TRIPLE))
-HB3 = $(HBIN3_H_$(CFG_HOST_TRIPLE))
+HB3 = $(HBIN2_H_$(CFG_HOST_TRIPLE))
 # Shorthand for build/stageN/lib
 HL = $(HLIB$(ISTAGE)_H_$(CFG_HOST_TRIPLE))
 # Shorthand for the prefix bin directory