[tor-bugs] #9869 [Tor]: configure runs tests with wrong tools for --host if suitable tools are not in $PATH

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#9869: configure runs tests with wrong tools for --host if suitable tools are not
in $PATH
-------------------------+-------------------------------------------------
     Reporter:  sqrt2    |      Owner:
         Type:  defect   |     Status:  needs_review
     Priority:  normal   |  Milestone:  Tor: 0.2.5.x-final
    Component:  Tor      |    Version:  Tor: unspecified
   Resolution:           |   Keywords:  armv6 curve25519 build tor-relay
Actual Points:           |  024-backport
       Points:           |  Parent ID:
-------------------------+-------------------------------------------------
Changes (by sqrt2):

 * status:  reopened => needs_review


Comment:

 The core of the issue is that autoconf is fairly bad at detecting whether
 it's cross compiling and has some strange attitudes about when to warn and
 when to error.

 Unless the user explicitly specifies --host ''and'' --build, it will say
 cross_compiling=maybe.

 AC_CHECK_TOOL actually detects that it could not find a properly named
 tool, and will print a warning, but only if cross_compiling==yes. We can
 cleanly check for whether that warning has been issued and error with a
 helpful error message instead.

 If cross_compiling==maybe however, things get ugly. As soon as AC_PROG_CC
 is run, autoconf will try to verify that it is cross-compiling by building
 a program and AC_TRY_RUN it. Because it will find any compiler on the
 system, however, it will also find the standard, non-cross, compiler, and
 come to the wrong conclusion cross_compiling=no. Since we check for the
 correct ar before running AC_PROG_CC, we can perform the same check that
 it would normally lead it to printing a warning and error with a helpful
 warning message instead. (I would argue that autoconf should at least warn
 here by default.)

 The patch I have posted above will implement this and give the user the
 option to --disable-tool-name-check to skip this test and continue with
 the tools found by AC_CHECK_TOOL.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/9869#comment:6>
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