build: remove -mretpoline and NO_EXTRA_CFLAGS

The -mretpoline flag is not documented in the current versions of gcc
and clang and it is what causes scan-build to fail:

    $ ./configure CC=clang | grep retpoline
    checking whether C compiler accepts -mretpoline... yes
       EXTRA_CFLAGS:  -mretpoline -fstack-clash-protection -fstack-protector-strong
    $ scan-build --status-bugs make
    scan-build: Using '/usr/bin/clang-15' for static analysis
    make -C src/lib
    make[1]: Entering directory '/tmp/firejail/src/lib'
    /usr/bin/../lib/clang/ccc-analyzer [...] -mretpoline [...] -c common.c -o common.o
    gcc: error: unrecognized command-line option ‘-mretpoline’
    make[1]: *** [../../src/prog.mk:16: common.o] Error 1
    make[1]: Leaving directory '/tmp/firejail/src/lib'
    make: *** [Makefile:59: src/lib] Error 2
    scan-build: Analysis run complete.
    scan-build: Removing directory '/tmp/scan-build-[...]' because it contains no reports.
    scan-build: No bugs found.

Environment: clang 15.0.7-9 and gcc 13.1.1-1 on Artix Linux.

Note: NO_EXTRA_CFLAGS was added to work around this issue by causing all
of the flags in EXTRA_CFLAGS to be ignored.

Note2: -mretpoline was added on commit 4a99c8aa2 ("spectre support for
clang compiler", 2018-03-30) and NO_EXTRA_CFLAGS was added on commit
490918c35 ("fix make scan-build for debian 10 and arch", 2019-07-22).
See also commit 2c64d1fdd ("use AX_CHECK_COMPILE_FLAG to check for
spectre flags", 2019-06-21).

Closes #5509.

Kind of relates to #2661.

1 files changed, 1 insertions, 1 deletions

diff --git a/Makefile b/Makefile
index c69c1894f..49c97c382 100644
--- a/Makefile
+++ b/Makefile
@@ -358,7 +358,7 @@ cppcheck: clean
 
 .PHONY: scan-build
 scan-build: clean
-        NO_EXTRA_CFLAGS="yes" scan-build make
+        scan-build make
 
 .PHONY: codespell
 codespell: clean