Use '\\' instead of "\\"

No real changes, just use simpler quoting construct which is sufficient
(as we don't need to expand any variables) and also happens not to break
Vim 8 syntax highlighting in the entire file, unlike double quotes.

Author: vadz

configure.ac

@@ -622,7 +622,7 @@ else
     PYEPREFIX=`($PYTHON -c "import sys; sys.stdout.write(sys.exec_prefix)") 2>/dev/null`
     AC_MSG_RESULT($PYEPREFIX)
 
-    if test x"$PYOSNAME" = x"nt" -a x"$PYSEPARATOR" = x"\\"; then
+    if test x"$PYOSNAME" = x"nt" -a x"$PYSEPARATOR" = x'\\'; then
       # Windows installations are quite different to posix installations (MinGW path separator is a forward slash)
       PYPREFIX=`echo "$PYPREFIX" | sed -e 's,\\\\,/,g'` # Forward slashes are easier to use and even work on Windows most of the time
       PYTHON_SO=.pyd
@@ -739,7 +739,7 @@ else
     PYVER=0
   fi
   if test "x$PY3BIN" = xyes; then
-    if test x"$PYOSNAME" = x"nt" -a x"$PYSEPARATOR" = x"\\" -a $PYVER -ge 3; then
+    if test x"$PYOSNAME" = x"nt" -a x"$PYSEPARATOR" = x'\\' -a $PYVER -ge 3; then
       PYTHON3="$PYTHON"
     else
       for py_ver in 3 3.9 3.8 3.7 3.6 3.5 3.4 3.3 3.2 ""; do
@@ -774,7 +774,7 @@ else
     PYSEPARATOR=`($PYTHON3 -c "import sys, os; sys.stdout.write(os.sep)") 2>/dev/null`
     AC_MSG_RESULT($PYSEPARATOR)
 
-    if test x"$PY3OSNAME" = x"nt" -a x"$PYSEPARATOR" = x"\\"; then
+    if test x"$PY3OSNAME" = x"nt" -a x"$PYSEPARATOR" = x'\\'; then
       # Windows installations are quite different to posix installations
       # There is no python-config to use
       AC_MSG_CHECKING(for Python 3.x prefix)