Preprocessed source stored into /tmp/cc3j4g1g.out file, please attach this to your bugreport.

Can you please provide one of these?

Definitely need the cpp output.

Created attachment 1386105 [details]
bz1538648-2.ii

Preprocessed sources from building audacious-plugins-3.9-4.fc28.

Compile with -march=i686 -fstack-clash-protection -O2.

Hm, I'm not sure how to get a file from a Fedora build machine. FWIW, a local build with gcc-7.2.1-7.fc28 works. Any chance it is related to bug #1536555, which was addressed in -8?

Created attachment 1386106 [details]
bz1538648-1.i

Preprocessed sources from chrony-3.2-2.fc28.

Compile with: -O2 -march=i686 -fstack-clash-protection

Obviously, we need to fix this, but an immediate workaround would be to switch to generic tuning (-mtune=generic) on i686, like we do on x86-64, via redhat-rpm-config.

That we run into this bug made me realize that we do not build i686 with generic tuning, as intended, and as is the GCC default (otherwise, we wouldn't have to specify -march=i686 explicitly to trigger this bug).

redhat-rpm-config-85-1.fc28 is now in the rawhide buildroot which activates generic tuning for i686, thus papering over all the instances of the bug I have seen so far.  (And stack clash protection is still enabled.)

Created attachment 1386187 [details]
Fixed librpm.so.8.0.1 for i686

librpm from rpm-4.14.1-3.fc28

To recover rpm on an affected i686 system, use these steps:

# curl https://bugzilla.redhat.com/attachment.cgi?id=1386187 > /usr/lib/librpm.so.8.0.1.new
# mv /usr/lib/librpm.so.8.0.1.new /usr/lib/librpm.so.8.0.1

After that, you can update rpm-libs regularly.

bz1538648-1.i also crashes with upstream GCC (trunk@257053):

during RTL pass: pro_and_epilogue
array.c: In function ‘ARR_CreateInstance’:
array.c:57:1: internal compiler error: in ix86_expand_prologue, at config/i386/i386.c:13740

Hope that can help something: 

https://kojipkgs.fedoraproject.org//work/tasks/9268/24439268/build.log

cd /builddir/build/BUILD/opencv-3.3.1/build/modules/core && /usr/bin/c++  -DCVAPI_EXPORTS -D_USE_MATH_DEFINES -D__OPENCV_BUILD=1 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -DHAVE_MALLOC_H=1 -DHAVE_MEMALIGN=1 -DHAVE_POSIX_MEMALIGN=1 -I/builddir/build/BUILD/opencv-3.3.1/build -isystem /usr/include/gdal -isystem /usr/include/eigen3 -isystem /usr/include/openblas -I/builddir/build/BUILD/opencv-3.3.1/modules/core/include -I/builddir/build/BUILD/opencv-3.3.1/modules/core/src -I/builddir/build/BUILD/opencv-3.3.1/build/modules/core  -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m32 -march=i686 -fasynchronous-unwind-tables -fstack-clash-protection -Wl,--as-needed   -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -pthread -march=i686 -fomit-frame-pointer -ffunction-sections  -msse -msse2 -mfpmath=sse -fvisibility=hidden -fvisibility-inlines-hidden -fPIC   -o CMakeFiles/opencv_core.dir/src/alloc.cpp.o -c /builddir/build/BUILD/opencv-3.3.1/modules/core/src/alloc.cpp

make[2]: Leaving directory '/builddir/build/BUILD/opencv-3.3.1/build'
*** WARNING *** there are active plugins, do not report this as a bug unless you can reproduce it without enabling any plugins.
Event                            | Plugins
PLUGIN_FINISH_UNIT               | Generate final annotations
PLUGIN_START_UNIT                | Generate global annotations
PLUGIN_ALL_PASSES_END            | Generate per-function annotations
/builddir/build/BUILD/opencv-3.3.1/modules/core/src/algorithm.cpp: In destructor 'cv::Algorithm::~Algorithm()':
/builddir/build/BUILD/opencv-3.3.1/modules/core/src/algorithm.cpp:56:1: internal compiler error: in ix86_expand_prologue, at config/i386/i386.c:14572
 }
 ^
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://bugzilla.redhat.com/bugzilla> for instructions.
{standard input}: Assembler messages:
{standard input}: Error: .size expression for algorithm.cpp does not evaluate to a constant
Preprocessed source stored into /tmp/ccmTqu4D.out file, please attach this to your bugreport.
make[2]: *** [modules/core/CMakeFiles/opencv_core.dir/build.make:93: modules/core/CMakeFiles/opencv_core.dir/src/algorithm.cpp.o] Error 1

Reduced test case from bz1538648-1.i (the size argument to the memcpy matters):

void
f (void *p1, void *p2)
{
  __builtin_memcpy (p1, p2, 1000);
}

Compile with: -O2 -m32 -march=i686 -fstack-clash-protection

*** Bug 1539625 has been marked as a duplicate of this bug. ***

FYI, owfs also failed with that:
https://kojipkgs.fedoraproject.org//work/tasks/9943/24599943/build.log

Only on i686, so it's not important.