[clang] clang -M should print expanded paths

[xtexx]

When using clang -M, some c++ standard library headers' paths are not real paths.

For example, on AOSC OS (a usr-merged Linux distribution), /bin/../lib64/gcc/ ... are emitted. These paths are valid for IO operations (/bin is linked to /usr/bin on usr-merged distributions, thus /bin/../lib64 is equivalent to /usr/lib64), but not for Make and Ninja. Both make and ninja canonicalize them to /lib64, which does not exist, and they always regards these targets as dirty and rebuilds them everytime.

xtex@xtex1 ~ (main)> cat test.cpp
#include <cstdio>

int main() { return 0; }
xtex@xtex1 ~ (main)> clang -M test.cpp
test.o: test.cpp \
  /bin/../lib64/gcc/x86_64-aosc-linux-gnu/13.2.0/../../../../include/c++/13.2.0/cstdio \
  /bin/../lib64/gcc/x86_64-aosc-linux-gnu/13.2.0/../../../../include/c++/13.2.0/x86_64-aosc-linux-gnu/bits/c++config.h \
  /bin/../lib64/gcc/x86_64-aosc-linux-gnu/13.2.0/../../../../include/c++/13.2.0/pstl/pstl_config.h \
  /usr/include/tbb/tbb.h /usr/include/stdio.h \
  /usr/include/bits/libc-header-start.h \
  /usr/lib/clang/18/include/stdarg.h \
(some paths are emitted)