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, 2 insertions, 2 deletions

diff --git a/src/prog.mk b/src/prog.mk
index b7ac59785..7797f56b6 100644
--- a/src/prog.mk
+++ b/src/prog.mk
@@ -5,8 +5,8 @@
 # The includer should probably define PROG and TARGET and may also want to
 # define EXTRA_HDRS and EXTRA_OBJS and extend CLEANFILES.
 
-HDRS := $(sort $(wildcard *.h)) $(EXTRA_HDRS)
-SRCS := $(sort $(wildcard *.c))
+HDRS := $(sort $(wildcard $(MOD_DIR)/*.h)) $(EXTRA_HDRS)
+SRCS := $(sort $(wildcard $(MOD_DIR)/*.c))
 OBJS := $(SRCS:.c=.o) $(EXTRA_OBJS)
 
 .PHONY: all