build: use full paths on compile/link targets

This makes the compile commands clearer when building in parallel (with
`make -j`) and ensures that `__FILE__` includes the full build-time path
(relative to the root of the repository) whenever it is referenced, such
as in failed assert() messages (currently the full path is only shown in
errExit() messages).  Example:

Before:

    firejail: main.c:100: main: Assertion `1 == 2' failed.
    Error src/firecfg/main.c:100: main: malloc: Cannot allocate memory

After:

    firejail: ../../src/firejail/main.c:100: main: Assertion `1 == 2' failed.
    Error ../../src/firecfg/main.c:100: main: malloc: Cannot allocate memory

Commands used to search and replace:

    $ git grep -Ilz '^MOD_DIR =' -- '*Makefile' | xargs -0 -I '{}' \
      sh -c "printf '%s\n' \"\$(sed -E \
        -e 's|^MOD_DIR = src/(.*)|MOD = \\1\\nMOD_DIR = \$(ROOT)/src/\$(MOD)|' \
        -e 's:^(PROG|SO) = [^.]+(\.so)?$:\\1 = \$(MOD_DIR)/\$(MOD)\2:' \
        '{}')\" >'{}'"
    $ git grep -Ilz '^HDRS :=' -- '*.mk' | xargs -0 -I '{}' \
      sh -c "printf '%s\n' \"\$(sed -E \
        -e 's|wildcard (\*\..)|wildcard \$(MOD_DIR)/\\1|' '{}')\" >'{}'"

Note: config.mk.in, src/fnettrace/Makefile and src/include/common.h were
edited manually.

This is a follow-up to #5871.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/fnet/Makefile b/src/fnet/Makefile
index 04a200951..c98326dc4 100644
--- a/src/fnet/Makefile
+++ b/src/fnet/Makefile
@@ -2,8 +2,9 @@
 ROOT = ../..
 -include $(ROOT)/config.mk
 
-MOD_DIR = src/fnet
-PROG = fnet
+MOD = fnet
+MOD_DIR = $(ROOT)/src/$(MOD)
+PROG = $(MOD_DIR)/$(MOD)
 TARGET = $(PROG)
 
 EXTRA_HDRS = ../include/common.h ../include/libnetlink.h