Commit 567962bd626 broke the Ubuntu on Windows build

[patacongo]

Eduard Niesner reported this problem: When building for Ubuntu on Windows, the build fails because all of the host tools are build with the .exe extension, in particulare, tools/mkconfig.exe. That fails because the binary with that extension is not recognized.

Steps to replicate:

• make distclean
• ./tools/configure.sh -u nucleo-h743zi:nsh
• make

Resulting error:

• /bin/sh: 1: tools/mkconfig: not found
• tools/Makefile.unix:247: recipe for target 'include/nuttx/config.h' failed
• make: *** [include/nuttx/config.h] Error 127

This error occurrs because the definitons of HOSTEXEXT is WRONG in tools/Config.mk:

116 ifeq ($(CONFIG_HOST_WINDOWS),y)
117   HOSTEXEEXT ?= .exe
118 endif

When Ubuntu it selects CONFIG_HOST_WINDOWS=y but the HOSTEXEEXT should be an empty string, not .exe. That is the root cause of the problem.

Commit 567962b introduced this error

commit 567962bd6263bf8809fb63c739f6ec668c69c416
Author: Xiang Xiao <[email protected]>
Date:   Tue May 19 18:29:28 2020 +0800

    build: Move the extension definition to common place

    Signed-off-by: Xiang Xiao <[email protected]>

This should be fixed before the 10.0 release and should be backported to the 9.1 release.