gcc/4.9: add patch to enable more C++ features with uClibc

This commit fixes bug #7250, by allowing more libstdc++ features to be
enabled with uClibc. libstdc++ wants an absolutely complete C99
support in the C library before enabling *any* feature that needs some
C99 functions. However, uClibc doesn't provide C99 complex numbers, so
libstdc++ disables a lot of C++ standard methods, even though they are
not related to C99 complex numbers.

A partial solution already existed in the patch
302-c99-snprintf.patch, but this commit replaces it by the more
complete 850-libstdcxx-uclibc-c99.patch, which is highly inspired by
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58393, except that it
doesn't rely on configure.ac checks, but simply on testing
defined(__UCLIBC__) like was done in 302-c99-snprintf.patch. This
allows to avoid having to autoreconf gcc, which is quite complicated
to achieve.

Reported-by: Richard <tarka.t.otter@gmail.com>
Cc: Richard <tarka.t.otter@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
gcc/4.9: fix C++ exceptions and pthread_exit()

Following the introduction of the support for the musl C library, the
support of C++ exceptions or features like pthread_exit() got broken
even with other libraries such as glibc. This was reported as bug #7028.

The problem was caused by the gcc patch needed to add support for
musl, which modified the libgcc/unwind-dw2-fde-dip.c logic to decide
whether USE_PT_GNU_EH_FRAME should be enabled or not. It completely
removed the existing logic, replacing it by a single logic based on
the definition of TARGET_DL_ITERATE_PHDR. However, this constant gets
defined by the configure script only for Solaris, or Linux Musl
platforms. For glibc/uClibc, the configure script does not define it,
and therefore USE_PT_GNU_EH_FRAME is not defined, causing issues with
exception handling.

This patch fixes that by restoring all the logic of
libgcc/unwind-dw2-fde-dip.c, and just adding the musl logic as one
more case.

It has been successfully runtime tested using the two code examples
provided in bug #7208, with uClibc, musl and glibc.

Cc: Krzysztof Wrzalik <kwrzalik@gmail.com>
Cc: David Bachelart <david.bachelart@bbright.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>