Defs.gmk contains rules to set BUILD_NUMBER if it is not set. The macro
uses $(ECHO) and $(USER), which have not necessarily been set. When building javac,
I get the following output, which is attributable to these values being undefined:

output:----------
/bin/sh: +%d_%b_%Y_%H_%M: not found
/bin/sh: A-Z: not found
/bin/sh: jjg_: not found
------------------

the macro in question:--------------
ifndef BUILD_NUMBER
# use ':=' to keep this value from changing as time marches on...
  BUILD_NUMBER := $(shell $(ECHO) $(USER)_`$(DATE) '+%d_%b_%Y_%H_%M' | $(TR) "A-Z" "a-z"`)
  JDK_BUILD_NUMBER = b00
else
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###@###.### 2004-11-11 23:06:05 GMT