Accommodate for the migration from MINGW64 to UCRT64

[dscho]

There was one thing that still needed changing: the CMake definition has no chance but to hard-code the MSYSTEM variable, and now it needs to be UCRT64 instead of MINGW64, otherwise t0060.221 fails:

failure: t0060.221 MSYSTEM/PATH is adjusted if necessary 
  	if test -z "$MINGW_PREFIX"
  	then
  		MINGW_PREFIX="/$(echo "${MSYSTEM:-MINGW64}" | tr A-Z a-z)"
  	fi &&
  	mkdir -p "$HOME"/bin pretend"$MINGW_PREFIX"/bin \
  		pretend"$MINGW_PREFIX"/libexec/git-core pretend/usr/bin &&
  	cp "$GIT_EXEC_PATH"/git.exe pretend"$MINGW_PREFIX"/bin/ &&
  	cp "$GIT_EXEC_PATH"/git.exe pretend"$MINGW_PREFIX"/libexec/git-core/ &&
  	# copy the .dll files, if any (happens when building via CMake)
  	if test -n "$(ls "$GIT_EXEC_PATH"/*.dll 2>/dev/null)"
  	then
  		cp "$GIT_EXEC_PATH"/*.dll pretend"$MINGW_PREFIX"/bin/ &&
  		cp "$GIT_EXEC_PATH"/*.dll pretend"$MINGW_PREFIX"/libexec/git-core/
  	fi &&
  	echo "env | grep MSYSTEM=" | write_script "$HOME"/bin/git-test-home &&
  	echo "echo ${MINGW_PREFIX#/}" | write_script pretend"$MINGW_PREFIX"/bin/git-test-bin &&
  	echo "echo usr" | write_script pretend/usr/bin/git-test-bin2 &&
  
  	(
  		MSYSTEM= &&
  		GIT_EXEC_PATH= &&
  		pretend"$MINGW_PREFIX"/libexec/git-core/git.exe test-home >actual &&
  		pretend"$MINGW_PREFIX"/libexec/git-core/git.exe test-bin >>actual &&
  		pretend"$MINGW_PREFIX"/bin/git.exe test-bin2 >>actual
  	) &&
  	test_write_lines MSYSTEM=$MSYSTEM "${MINGW_PREFIX#/}" usr >expect &&
  	test_cmp expect actual
  
  ++ test -z ''
  +++ echo UCRT64
  +++ tr A-Z a-z
  ++ MINGW_PREFIX=/ucrt64
  ++ mkdir -p '/d/a/git/git/t/trash directory.t0060-path-utils/bin' pretend/ucrt64/bin pretend/ucrt64/libexec/git-core pretend/usr/bin
  ++ cp /d/a/git/git/git.exe pretend/ucrt64/bin/
  ++ cp /d/a/git/git/git.exe pretend/ucrt64/libexec/git-core/
  +++ ls /d/a/git/git/charset-1.dll /d/a/git/git/iconv-2.dll /d/a/git/git/legacy.dll /d/a/git/git/libcrypto-3-x64.dll /d/a/git/git/libcurl.dll /d/a/git/git/libexpat.dll /d/a/git/git/libssh2.dll /d/a/git/git/libssl-3-x64.dll /d/a/git/git/z.dll
  ++ test -n $'/d/a/git/git/charset-1.dll\n/d/a/git/git/iconv-2.dll\n/d/a/git/git/legacy.dll\n/d/a/git/git/libcrypto-3-x64.dll\n/d/a/git/git/libcurl.dll\n/d/a/git/git/libexpat.dll\n/d/a/git/git/libssh2.dll\n/d/a/git/git/libssl-3-x64.dll\n/d/a/git/git/z.dll'
  ++ cp /d/a/git/git/charset-1.dll /d/a/git/git/iconv-2.dll /d/a/git/git/legacy.dll /d/a/git/git/libcrypto-3-x64.dll /d/a/git/git/libcurl.dll /d/a/git/git/libexpat.dll /d/a/git/git/libssh2.dll /d/a/git/git/libssl-3-x64.dll /d/a/git/git/z.dll pretend/ucrt64/bin/
  ++ cp /d/a/git/git/charset-1.dll /d/a/git/git/iconv-2.dll /d/a/git/git/legacy.dll /d/a/git/git/libcrypto-3-x64.dll /d/a/git/git/libcurl.dll /d/a/git/git/libexpat.dll /d/a/git/git/libssh2.dll /d/a/git/git/libssl-3-x64.dll /d/a/git/git/z.dll pretend/ucrt64/libexec/git-core/
  ++ echo 'env | grep MSYSTEM='
  ++ write_script '/d/a/git/git/t/trash directory.t0060-path-utils/bin/git-test-home'
  ++ echo '#!/bin/sh'
  ++ cat
  ++ chmod +x '/d/a/git/git/t/trash directory.t0060-path-utils/bin/git-test-home'
  ++ echo 'echo ucrt64'
  ++ write_script pretend/ucrt64/bin/git-test-bin
  ++ echo '#!/bin/sh'
  ++ cat
  ++ chmod +x pretend/ucrt64/bin/git-test-bin
  ++ echo 'echo usr'
  ++ write_script pretend/usr/bin/git-test-bin2
  ++ echo '#!/bin/sh'
  ++ cat
  ++ chmod +x pretend/usr/bin/git-test-bin2
  ++ MSYSTEM=
  ++ GIT_EXEC_PATH=
  ++ pretend/ucrt64/libexec/git-core/git.exe test-home
  ++ pretend/ucrt64/libexec/git-core/git.exe test-bin
  git: 'test-bin' is not a git command. See 'git --help'.
  error: last command exited with $?=1
  not ok 221 - MSYSTEM/PATH is adjusted if necessary
  #	
  #		if test -z "$MINGW_PREFIX"
  #		then
  #			MINGW_PREFIX="/$(echo "${MSYSTEM:-MINGW64}" | tr A-Z a-z)"
  #		fi &&
  #		mkdir -p "$HOME"/bin pretend"$MINGW_PREFIX"/bin \
  #			pretend"$MINGW_PREFIX"/libexec/git-core pretend/usr/bin &&
  #		cp "$GIT_EXEC_PATH"/git.exe pretend"$MINGW_PREFIX"/bin/ &&
  #		cp "$GIT_EXEC_PATH"/git.exe pretend"$MINGW_PREFIX"/libexec/git-core/ &&
  #		# copy the .dll files, if any (happens when building via CMake)
  #		if test -n "$(ls "$GIT_EXEC_PATH"/*.dll 2>/dev/null)"
  #		then
  #			cp "$GIT_EXEC_PATH"/*.dll pretend"$MINGW_PREFIX"/bin/ &&
  #			cp "$GIT_EXEC_PATH"/*.dll pretend"$MINGW_PREFIX"/libexec/git-core/
  #		fi &&
  #		echo "env | grep MSYSTEM=" | write_script "$HOME"/bin/git-test-home &&
  #		echo "echo ${MINGW_PREFIX#/}" | write_script pretend"$MINGW_PREFIX"/bin/git-test-bin &&
  #		echo "echo usr" | write_script pretend/usr/bin/git-test-bin2 &&
  #	
  #		(
  #			MSYSTEM= &&
  #			GIT_EXEC_PATH= &&
  #			pretend"$MINGW_PREFIX"/libexec/git-core/git.exe test-home >actual &&
  #			pretend"$MINGW_PREFIX"/libexec/git-core/git.exe test-bin >>actual &&
  #			pretend"$MINGW_PREFIX"/bin/git.exe test-bin2 >>actual
  #		) &&
  #		test_write_lines MSYSTEM=$MSYSTEM "${MINGW_PREFIX#/}" usr >expect &&
  #		test_cmp expect actual
  #	

The reason is that MSYSTEM/MINGW_PREFIX are left unset, specifically to verify that git.exe hard-codes the correct values. Let's make that adjustment so that vs-test has a chance of passing again.