scripts: fix dumping execution backtrace

Dumping the backtrace has been broken since changeset #652e56d6d35a:
scripts: execute each steps in a subshell

We can spawn sub-sub-shells in some cases.

The way the fault handler works is to dump the backtrace, but to avoid
printing it once for every sub-shell (which could get quite confusing),
it simply exits when it detects that it is being run in a sub-shell,
leaving to the top-level shell the work to dump the backtrace.

Because each step is executed in its own sub-shell, the variable arrays
that contain the step name, the source file and line number, are lost
when exiting the per-step sub-shell.

Hence, the backtrace is currently limited to printing only the top-level
main procedure of the shell.

Fix this thus:
- when dumping the bckatraces for the steps & the functions, remember
it was dumped, and only dump it if it was not already dumped
- at the top-level shell, print the hints

Also, rename the top-level step label.

Reported-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from 4193d6e6a17430a177fa88c287879c2c35e319f3)

Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org> wrote:

I tried to use crosstool-ng to generate a toolchain for Linux on big

endian arm with recent versions of gcc, glibc, etc... but had a few

problems.

It appears that the gcc patch (for gcc 4.2.x)

for big-endian arm (240-arm-bigendian.patch) lacks the change attached

to this mail as 240-arm-bigendian2.patch.

--- gcc-4.2.4/gcc/config/arm/bpabi.h~	2007-09-01 17:28:30.000000000 +0200

+++ gcc-4.2.4/gcc/config/arm/bpabi.h	2009-01-05 19:19:10.000000000 +0100

@@ -32,9 +32,19 @@

 #undef FPUTYPE_DEFAULT

 #define FPUTYPE_DEFAULT FPUTYPE_VFP

+/*

+ * 'config.gcc' defines TARGET_BIG_ENDIAN_DEFAULT as 1 for arm*b-*

+ * (big endian) configurations.

+ */

+#if TARGET_BIG_ENDIAN_DEFAULT

+#define TARGET_ENDIAN_DEFAULT MASK_BIG_END

+#else

+#define TARGET_ENDIAN_DEFAULT 0

+#endif

+

 /* EABI targets should enable interworking by default.  */

 #undef TARGET_DEFAULT

-#define TARGET_DEFAULT MASK_INTERWORK

+#define TARGET_DEFAULT (MASK_INTERWORK | TARGET_ENDIAN_DEFAULT)

 /* The ARM BPABI functions return a boolean; they use no special

    calling convention.  */