RFR: JDK-8075054 Mixed case Windows path break native dependency checks

[Magnus Ihse Bursie]

Bug description:

If the top-level directory of the forest contains mixed case elements in 
the path, then the script which checks for native C/C++ headers 
dependencies doesn't work properly.
This happens because Visual Studio compiler sometimes (?) produce 
lower-case only paths when invoked with the -showIncludes option used in 
the dependency tracking, and the script doesn't match these paths with 
the mixed case paths produced from the top-level directory.

For example, if the top-level directory is /cygdrive/c/Vadim/jdk9, then 
the cl.exe invocation cmdline looks like this:
/cygdrive/c/Vadim/jdk9/.../fixpath.exe -c ...cl ... -c -showIncludes ... 
/cygdrive/c/Vadim/jdk9/...foo.cpp | tee ... foo.d.raw
The .d.raw file contains these lines (note the lowercase path):
Note: including file: 
c:\vadim\jdk9-cpu\jdk\src\java.desktop\share\native\foo.h

My proposed fix:

diff --git a/make/common/NativeCompilation.gmk 
b/make/common/NativeCompilation.gmk
--- a/make/common/NativeCompilation.gmk
+++ b/make/common/NativeCompilation.gmk
@@ -60,7 +60,7 @@
      -e 's|Note: including file: *||' \
      -e 's|\\|/|g' \
      -e 's|^\([a-zA-Z]\):|$(UNIX_PATH_PREFIX)/\1|g' \
-    -e '/$(subst /,\/,$(TOPDIR))/!d' \
+    -e '\|$(TOPDIR)|I !d' \
      -e 's|$$$$| \\|g' \
      #

@@ -153,7 +153,7 @@
               exit `cat $$($1_$2_DEP).exitvalue`
           $(RM) $$($1_$2_DEP).exitvalue
           ($(ECHO) $$@: \\ \
-         && $(SED) $(WINDOWS_SHOWINCLUDE_SED_PATTERN) 
$$($1_$2_DEP).raw) > $$($1_$2_DEP)
+         && $(SED) $(WINDOWS_SHOWINCLUDE_SED_PATTERN) 
$$($1_$2_DEP).raw) | $(SORT) -u > $$($1_$2_DEP)
          endif
          # Create a dependency target file from the dependency file.
          # Solution suggested by 
http://make.mad-scientist.net/papers/advanced-auto-dependency-generation/

Some comments might be warranted.

I learned a bit about sed expressions when fixing this. :) For those who 
didn't know, sed expressions consists of two parts, an "address" and a 
"command". A typical "s/foo/bar/" is just the command "s" with some 
arguments. The "s" command allows the separator to be changed from / to 
anything else, eg "s!foo!bar!", and without an address, it works on all 
lines.

The problematic line is instead using the "d" (delete), or more 
precisely, the "!d" (not delete) command. The expression in front is the 
"address", which in this case is a regexp. So lines matching the regexp 
would not be deleted (but all others will). Since TOPDIR contains 
slashes, the old expression used make $(subst) to espace these slashes, 
so they wouldn't be interpreted as ending the address regexp. A better 
solution is to use a different character, but for the address, this 
require the regexp to be preceeded by a backslash. Hence, e.g. "\|foo| 
d" would delete all lines matching foo.

After the expression is what solves this bug. It is an uppercase I, 
which is a GNU sed extension to make the regexp case insensitive. While 
it is available in GNU sed only, this is not a problem since it's only 
being used on Windows, where only GNU sed is supported.

The second changed line is strictly not needed to fix the bug, but 
removes the prolific duplication of header files that the .d files had 
on Windows before, drastically reducing them in size.

Bug: https://bugs.openjdk.java.net/browse/JDK-8075054

/Magnus