The Java SE build log for mustang contains a number of messages like this:

  gnumake[1]: Entering directory `/export/u5/b65PIT/j2se/make/java'
  Begin Processing SUBDIRS: hpi version jvm redist verify fdlibm java sun_nio jli main zip javac javah security npt java_crw_demo java_hprof_demo math awt util text applet net nio sql rmi jar beans logging management instrument jexec
  >>>Recursively making hpi all @ Mon Dec 19 20:08:30 PST 2005 ...
  expr: syntax error
  gnumake[2]: Entering directory `/export/u5/b65PIT/j2se/make/java/hpi'
  Begin Processing SUBDIRS: native
  >>>Recursively making native all @ Mon Dec 19 20:08:31 PST 2005 ...
  expr: syntax error
  gnumake[3]: Entering directory `/export/u5/b65PIT/j2se/make/java/hpi/native'
   [...]
  Begin parallel compiles: /export/u5/b65PIT/j2se/make/java/hpi/native
  expr: syntax error
  gnumake[4]: Entering directory `/export/u5/b65PIT/j2se/make/java/hpi/native'
   [...]
  gnumake[4]: Leaving directory `/export/u5/b65PIT/j2se/make/java/hpi/native'
  Done with parallel compiles: /export/u5/b65PIT/j2se/make/java/hpi/native
   [...]
  gnumake[3]: Leaving directory `/export/u5/b65PIT/j2se/make/java/hpi/native'
  <<<Finished Recursively making native all @ Mon Dec 19 20:08:40 PST 2005.
  Done Processing SUBDIRS: native
  gnumake[2]: Leaving directory `/export/u5/b65PIT/j2se/make/java/hpi'
  <<<Finished Recursively making hpi all @ Mon Dec 19 20:08:40 PST 2005.
  >>>Recursively making version all @ Mon Dec 19 20:08:40 PST 2005 ...
  expr: syntax error
  gnumake[2]: Entering directory `/export/u5/b65PIT/j2se/make/java/version'


This clutters the build with additional warnings.

The fact that the build continues and is ultimately successful is
probably due to good luck.