make-3.81: bug-report: function abspath works incorrectly on widows

[Vitaly Murashev]

Hello, FSF community.
I found a bug in GNU Make 3.81 on MS Windows. So let me discuss it and
suggest a patch.

The problem take place in function abspath when trying to expand paths
which are already full qualified.

makefile for test is the next:
---
$(info test - $(abspath C:/))
$(info test - $(abspath C:))
$(info test - $(abspath C:/Windows/system32/))
$(info test - $(abspath C:/Windows/system32/..))
$(info test - $(abspath C:/Windows/system32/../..))
$(info test - $(abspath C:/../../))
$(info test - $(abspath C:/../..))
$(info test - $(abspath .))
$(info test - $(abspath ../..))
---

Output with Gnu Make 3.81 (current directory is H:/make-3.81):
---
test - H:/make-3.81/C:
test - H:/make-3.81/C:
test - H:/make-3.81/C:/Windows/system32
test - H:/make-3.81/C:/Windows
test - H:/make-3.81/C:
test - H:
test - H:
test - H:/make-3.81
test - H:/make-3.81
make: *** No targets.  Stop.
---

Output after apppling my patch for the function.c :
---
test - C:
test - C:
test - C:/Windows/system32
test - C:/Windows
test - C:
test - C:
test - C:
test - h:/make-3.81
test - h:
make_msvc.net2003: *** No targets.  Stop.
---
Suggested patch is in attachment.

function.c.patch
Description: Binary data