libgo: add "vendor" to pkgpath for vendored standard packages

Ensure that the packages vendored into the standard library do not
    have the same pkgpath as the actual packages.  If we don't, attempts
    to build and test the actual packages will get confused.  The specific
    error I was seeing was import loops, causing some of the packages to
    fail to get initialized, causing an obscure run time crash.
    
    Reviewed-on: https://go-review.googlesource.com/43610

From-SVN: r248168

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-924a1fcc5658a5d66f5015921d7258e3a77519bc
+ba68a42618d1e8516e38da093d3af731d7fd4f06
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/Makefile.am

@@ -910,7 +910,7 @@ BUILDDEPS = \
 BUILDPACKAGE = \
 	$(MKDIR_P) $(@D); \
 	files=`echo $^ | sed -e 's/[^ ]*\.gox//g' -e 's/[^ ]*\.dep//'`; \
-	$(LTGOCOMPILE) -I . -c -fgo-pkgpath=`echo $@ | sed -e 's/.lo$$//'` $($(subst -,_,$(subst .,_,$(subst /,_,$@)))_GOCFLAGS) -o $@ $$files
+	$(LTGOCOMPILE) -I . -c -fgo-pkgpath=`echo $@ | sed -e 's/.lo$$//' -e 's|golang_org|vendor/golang_org|'` $($(subst -,_,$(subst .,_,$(subst /,_,$@)))_GOCFLAGS) -o $@ $$files
 
 # How to build a .gox file from a .lo file.
 # Matching .o file can either be in the same directory as the .lo (non-PIC

libgo/Makefile.in

@@ -1063,7 +1063,7 @@ BUILDDEPS = \
 BUILDPACKAGE = \
 	$(MKDIR_P) $(@D); \
 	files=`echo $^ | sed -e 's/[^ ]*\.gox//g' -e 's/[^ ]*\.dep//'`; \
-	$(LTGOCOMPILE) -I . -c -fgo-pkgpath=`echo $@ | sed -e 's/.lo$$//'` $($(subst -,_,$(subst .,_,$(subst /,_,$@)))_GOCFLAGS) -o $@ $$files
+	$(LTGOCOMPILE) -I . -c -fgo-pkgpath=`echo $@ | sed -e 's/.lo$$//' -e 's|golang_org|vendor/golang_org|'` $($(subst -,_,$(subst .,_,$(subst /,_,$@)))_GOCFLAGS) -o $@ $$files
 
 
 # How to build a .gox file from a .lo file.