If you install the latest CYGWIN with make 3.81-1, you can't use this version of make to build the JDK anymore:
  bash-3.1$ make
  common/Release.gmk:412: *** target pattern contains no `%'. Stop.
Apparently this version of make doesn't support MSDOS path names that use the ':' character, which is probably being confused with the target/dependency character.

The JDK make file j2se/make/common/Release.gmk has many targets that are full paths, and these will have path names like C:/temp.

Many of the tools used in the makefiles during the JDK build only understand the C:/ or C:\ pathnames (the JDK 6 makefiles all use the C:/ pathnames) like the Microsoft Visual Studio compiler, any Windows/Microsoft native tools, and our own java/java/javah/jar tools. So use if the /cygdrive/c/ style pathnames will not work in all cases.