Always create a .eh_frame section even if it's empty

glibc's `__register_frame_info_bases` expect that it can read a terminator
if a .eh_frame is empty. Removing the section completely caused a crash bug
on Alpine Linux with musl as libc.

Specifically, mold-generated binaries crash if all the following
condition were met:

 1. musl is used as a libc
 2. .eh_frame is empty
 3. libgcc_s.so is linked

Prior to 06b5926, condition (3) was not
usually satisfied, so we didn't notice this issue. Now, the shared library
is linked against almost all output files because the file is referenced by
`__deregister_frame_info`.

https://github.com/bminor/glibc/blob/910aae6e5a2196938fc30fa54dd1e96f16774ce7/sysdeps/generic/unwind-dw2-fde.c#L105-L107

Fixes #1309

elf/output-chunks.cc

@@ -2208,14 +2208,6 @@ template <typename E>
 void EhFrameSection<E>::construct(Context<E> &ctx) {
   Timer t(ctx, "eh_frame");
 
-  // If .eh_frame is missing in all input files, we don't want to
-  // create an output .eh_frame section.
-  if (std::all_of(ctx.objs.begin(), ctx.objs.end(),
-                  [](ObjectFile<E> *file) { return file->cies.empty(); })) {
-    this->shdr.sh_size = 0;
-    return;
-  }
-
   // Remove dead FDEs and assign them offsets within their corresponding
   // CIE group.
   tbb::parallel_for_each(ctx.objs, [&](ObjectFile<E> *file) {