BaseTools: Remove caret in NASM_INC macro

BaseTools: Remove caret in NASM_INC macro

NASM_INC contains the list of directory to include when using
the nasm assembler.

In nmake makefiles, a trailing backslash escapes the newline char
and replaces it with a space ' '. To have a literal trailing
backslash, it must be escaped with a caret '^'. This is not
necessary for GNU makefiles.

On windows platforms, for the NASM_INC macro, a caret escaping
a trailing a backslash was appended to the last included
folder regardless of the makefile type.
For instance, "/Include/" was replaced by "/Include/^\".

This is causing a build failure on windows platforms using
GNU makefiles since the caret '^' doesn't escape any chars in
GNU makefiles and is thus conserved.
"/Include^\" was replaced by "/Include\/" in nmake makefiles,
but remained "/Include/^\" in GNU makefiles.

This patch removes the caret '^' on the build using GNU makefiles.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>