[Bug libstdc++/40974] cannot build gcc-4.4.1: fenv_t has not been declared

[armand dot potter at free dot fr]

------- Comment #31 from armand dot potter at free dot fr  2010-07-21 21:35 -------
I made some more investigations (a bit late as I am using now
--disable-libpchstdcxx like everyone else). IMHO three main options are
possible :

1/ Use -nostdinc++ just as native compilers do. Like said in comment #28, it
may break if used cross-compiler is incompatible with in-tree c++ headers (can
gcc be built that way ?)

2/ Do not use in-tree headers when using a cross-compiler. Not sure it is a
good solution and it may break if cross-compiler does not provide correct c++
headers.

3/ Use -I=\${includedir} just as when doing canadian cross compilations (see
comment #17). Note that I am building a native compiler that runs on another
host that the one building it (is that also canadian cross compilation no ?) so
-I\${includedir} should be included. It is not because this test fails in
libstdc++-v3/configure.ac :

  if test -n "$with_cross_host" &&
     test x"$build_alias" != x"$with_cross_host" &&
     test x"$build" != x"$target";

and this test fails because with-cross-host is not defined in ./configure.ac as
host = target (but build != host). Test should be on host (cross_host seems to
be deprecated). Also for 3/ to work, '=' needs to be added to -I\${includedir}
to force cross-compiler to use sysroot path and to avoid including native
headers from build system.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40974