Fix RPM packaging for modern openSUSE Leap 16, Fedora, and RHEL/Rocky Linux

[leotada]

Summary of Changes

This PR modernizes the RPM packaging in linux/dmd_rpm.sh to fix compatibility on openSUSE Leap 16, openSUSE Tumbleweed, Rocky Linux / RHEL, and Fedora:

1. RPM Boolean Rich Dependencies (Requires:):

   • Replaced distro-specific names with explicit boolean dependencies: (libcurl($FARCH) or libcurl4($FARCH)) and (libgcc($FARCH) or libgcc_s1($FARCH)).
   • On openSUSE Leap 16+, libcurl4 is used (there is no libcurl or libcurl4-32bit). On Fedora/RHEL, libcurl is used. This allows the RPM packages to be cross-compatible across all RPM-based distros.

2. 32-bit Multilib Isolation & Weak Dependencies (Recommends:):

   • Bundled 32-bit Phobos (/usr/lib/libphobos2.so*) previously caused RPM's find-requires to inject an automatic 32-bit Requires: libgcc_s.so.1 into the 64-bit package, which fails on standard 64-bit systems where 32-bit libgcc_s.so.1 is not installed by default. Added %global __requires_exclude_from ^/usr/lib/libphobos2\\.so.*$ on x86_64 to prevent this leak.
   • Converted 32-bit development dependencies (glibc-devel(x86-32) or glibc-devel-32bit, libgcc(x86-32) or libgcc_s1-32bit, libcurl(x86-32) or libcurl4-32bit) from hard Requires: to Recommends:. This prevents installation failures on 64-bit-only installations while still pulling in multilib packages when requested/available.
   • Fixed typo in openSUSE 32-bit dependencies: gcc-32bit($FARCH) evaluated to non-existent gcc-32bit(x86-64).

3. Smooth openSUSE Upgrades (Provides: & Obsoletes:):

   • Added Provides and Obsoletes for phobos-devel, phobos-devel-static, and dub to prevent file conflicts when upgrading over openSUSE's distribution-split packages.

4. Build System Compatibility:

   • Updated OS verification to recognize /etc/os-release so dmd_rpm.sh can be executed on any modern Linux distribution.
   • Made fakeroot optional if rpmbuild is already installed.
   • Defined _topdir and _tmppath to ensure clean builds in unprivileged or containerized build environments.

[dejlek]

Tested this in incus containers on Fedora 44, openSUSE Leap 16.0, Tumbleweed, AlmaLinux 8 & 9 (dmd 2.110.0). Works, one bug to fix.

Verified working

• __requires_exclude_from fix: A/B build on Leap 16 confirmed the 32-bit libphobos2.so in /usr/lib leaks ld-linux.so.2, libgcc_s.so.1, … into the x86_64 package without it; clean with it. (rpm 6/Fedora never leaks; this matters on rpm 4.x.)
• Rich deps parse and resolve on all 5 distros; fresh install + dmd -run test_curl.d passes on all.
• Leap 16 upgrade over the distro split stack (dmd/phobos-devel/phobos-devel-static/dub/libphobos2-0_109) replaces it cleanly, no file conflicts.
• fakeroot-optional path, _topdir/_tmppath defines, dub --version extraction all work.

Bug

• Obsoletes: libphobos2-0_109 is hardcoded but this script builds every release. A 2.110 build has soname libphobos2.so.0.110 yet obsoletes libphobos2-0_109; Tumbleweed already ships libphobos2-0_113. Derive it instead:
  PHOBOS_LIB_PKG="libphobos2-$(echo $SO_VERSION | tr . _)"

Nits

• Recommends are installed by default (dnf/zypper weak deps): 32-bit multilib is still pulled on Fedora/EL (verified: glibc-devel/libgcc/libcurl i686 + deps). Use Suggests: for "only when requested", or reword the PR description.
• DUB_VER=$VERSION fallback mixes namespaces (dub = 2.110.0-0); and Obsoletes: dub < $DUB_VER misses when the distro dub is newer than bundled (e.g. TW 1.42 vs bundled 1.39) → /usr/bin/dub conflict remains.
• The os-release check is now vacuous (every distro has /etc/os-release) — drop it or check ID_LIKE.
• README "installable on fedora/rhel/centos/rocky": rich deps need rpm ≥ 4.13, so RHEL 7 can't install it — say "RHEL/Rocky 8+".

Fix the Bug and it should be good to merge!