compilers: do not strip '-isystem' from C build arguments

Meson accidentally strips '-isystem' from C build args like ['-isystem',
'/path/to/headers'] if the compiler includes the current working directory
in the header search paths. The root cause is that '-isystem'[8:] evaluates
to an empty string and os.path.realpath('') returns the absolute path to
the current working directory, causing meson to think that '-isystem'
specifies a default include path.

Different compiler versions varies whether the current working directory is
in its search paths. For example, on Ubuntu 21.04:

  # gcc -xc -v -E -
  gcc version 10.3.0 (Ubuntu 10.3.0-1ubuntu1)
  #include "..." search starts here:
  #include <...> search starts here:
   .
   /usr/lib/gcc/x86_64-linux-gnu/10/include
   /usr/local/include
   /usr/include/x86_64-linux-gnu
   /usr/include
  End of search list.

While on Ubuntu 24.04:

  # gcc -xc -v -E -
  gcc version 13.2.0 (Ubuntu 13.2.0-23ubuntu4)
  ...
  #include "..." search starts here:
  #include <...> search starts here:
   /usr/lib/gcc/x86_64-linux-gnu/13/include
   /usr/local/include
   /usr/include/x86_64-linux-gnu
   /usr/include
  End of search list.

Do not check the '-isystem=' and '-isystem/path/to/header' cases when the
option is '-isystem' but the path that follows is not a default search
path.

Signed-off-by: Junjie Mao <junjie.mao@hotmail.com>

0 files changed, 0 insertions, 0 deletions