gcc.info: Header Dirs

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Standard Header File Directories

   `GCC_INCLUDE_DIR' means the same thing for native and cross.  It is
where GNU CC stores its private include files, and also where GNU CC
stores the fixed include files.  A cross compiled GNU CC runs
`fixincludes' on the header files in `$(tooldir)/include'.  (If the
cross compilation header files need to be fixed, they must be installed
before GNU CC is built.  If the cross compilation header files are
already suitable for ANSI C and GNU CC, nothing special need be done).
   `GPLUSPLUS_INCLUDE_DIR' means the same thing for native and cross.
It is where `g++' looks first for header files.  The C++ library
installs only target independent header files in that directory.
   `LOCAL_INCLUDE_DIR' is used only for a native compiler.  It is
normally `/usr/local/include'.  GNU CC searches this directory so that
users can install header files in `/usr/local/include'.
   `CROSS_INCLUDE_DIR' is used only for a cross compiler.  GNU CC
doesn't install anything there.
   `TOOL_INCLUDE_DIR' is used for both native and cross compilers.  It
is the place for other packages to install header files that GNU CC will
use.  For a cross-compiler, this is the equivalent of `/usr/include'.
When you build a cross-compiler, `fixincludes' processes any header
files in this directory.