Errors during make check 2.0.0_p247 on RH Linux

Hello,

I searched the Ruby forum and other Googling without success :-(
Target machine RH Enterprise Linux Version 6, 64-bit, with latest
patches.
Ruby 2.0.0_p247 source
"./compile" shows no errors or warnings
"make" shows some errors such as:
<quote>
/opt/ruby-2.0.0-p247/include/ruby/ruby.h:24: Warning: include file
ruby/config.h not found, perhaps you forgot to add its directory to
INCLUDE_PATH?
<unquote>

I have set an environment variable INCLUDE_PATH to
/opt/ruby-2.0.0_p247/include without any improvement.   Apart from
mentions about Doxyfile I cannot see any other references to
INCLUDE_PATH in the source directory tree.

Ignoring those errors for the time being, a subsequent "make check" runs
a huge number of checks without error.   Some errors do show up though
in, for example,

<quote>
TestFind#test_unsearchable_dir = 0.00 s
  2) Failure:
test_unsearchable_dir(TestFind)
[/opt/ruby-2.0.0-p247/test/test_find.rb:119]:
Errno::EACCES expected but nothing was raised.
<unquote>

Is this behaviour indicative of a missing library (at the OS level?)   I
have added just about all the -dev libraries I can think of via yum.
Insights appreciated.

FWIW I am used to compiling from source, mainly on Debian / Ubuntu over
many years and nothing leaps out to me as obvious, otherwise I wouldn't
be bothering you :-(

Kind regards,
Denis

P.S. Could retreat to an earlier version (e.g. 1.9.3) if that would
help, but would like to use the latest stable if possible.

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