[Bug other/90655] New: make install fails with empty DESTDIR on cygwin

[helmut.grohne at intenta dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90655

            Bug ID: 90655
           Summary: make install fails with empty DESTDIR on cygwin
           Product: gcc
           Version: 8.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: helmut.grohne at intenta dot de
  Target Milestone: ---
              Host: x86_64-w64-mingw32
             Build: x86_64-pc-cygwinng

Created attachment 46425
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46425&action=edit
patch for trunk

When running make install with an empty DESTDIR, a small number of install
invocations will attempt to install to $(DESTDIR)/$(something) where something
typically is one of libdir, includedir or plugin_resourcesdir. All of these
typically start with ${prefix} which starts with a slash. When DESTDIR is
empty, the whole path starts with two forward slashes. Cygwin has a special
handling for paths that start with two forward slashes and interprets them as
network shares (see https://unix.stackexchange.com/a/12291/259352). The
relevant install invocations fail. This affects a small number of install
invocations in c, cp, jit and lto. The majority of install invocations use
$(DESTDIR)$(something), which works fine on cygwin.