Do not hard-code paths for the shell and perl.

The reason to set SHELL_PATH and PERL_PATH was that 'make' failed to
execute
	/bin/sh some-script

It turns out that different MinGW/MSYS environments have different
levels of support for this construct, so use the default and let the user
override the settings in config.mak if the defaults don't work.

Makefile

@@ -475,8 +475,6 @@ ifeq ($(uname_S),IRIX64)
 	BASIC_LDFLAGS += -L/usr/lib32
 endif
 ifneq (,$(findstring MINGW,$(uname_S)))
-	SHELL_PATH = $(shell cd /bin && pwd -W)/sh
-	PERL_PATH = $(shell cd /bin && pwd -W)/perl
 	NO_MMAP=YesPlease
 	NO_PREAD=YesPlease
 	NO_OPENSSL=YesPlease

README.MinGW

@@ -31,6 +31,13 @@ In order to compile this code you need:
 	libiconv-1.9.2-1-{lib,bin,lib}.zip (for git-am,
 		from http://gnuwin32.sourceforge.net/packages/libiconv.htm)
 
+I am using these settings in config.mak to have pointers to the right tools:
+
+TCL_PATH=tclsh84
+TCLTK_PATH=wish84
+SHELL_PATH=D:/MSYS/1.0/bin/sh
+PERL_PATH=D:/MSYS/1.0/bin/perl
+
 
 STATUS
 ------