devel:18/pg_tde: pull gcc-c++ into SUSE chroots for the C++ KMIP client

Upstream commit 844379e (post-2.2.1) made pg_tde need a C++ compiler for
the new C++ KMIP client library. On openSUSE Tumbleweed and Leap 16 the
spec never installed one, so meson fell back to clang++ (present only via
the llvmjit BuildRequires) while C was still compiled by gcc. With SUSE's
default -flto=auto that mixed toolchain cannot be linked: gcc-ar cannot
index clang LLVM bitcode archives and clang's ld.bfd cannot read gcc LTO
objects, failing with

  libkmipclient.a: error adding symbols: archive has no index
  plugin needed to handle lto object

Add gcc-c++ to the suse_version BuildRequires so meson picks c++ (g++)
and the whole build uses one toolchain.

Verified in a Tumbleweed container against the published staging:18 repo
with clang installed and -flto=auto in C/CXX/LDFLAGS: meson selects
c++ (gcc 15.3.0), all targets link, pg_tde.so is produced.

Signed-off-by: Ricardo Dias <ricardo.dias@percona.com>

Author: rjd15372

root/ppg/devel/18/percona-pg_tde/rpm/pg_tde.spec

@@ -38,6 +38,11 @@ BuildRequires:	json-c-devel lz4-devel libzstd-devel numactl-devel
 %endif
 %if 0%{?suse_version}
 BuildRequires:	libjson-c-devel liblz4-devel libzstd-devel >= 1.4.0 libnuma-devel
+# The C++ KMIP client needs a C++ compiler. Without gcc-c++ in the chroot
+# meson falls back to clang++ (pulled in via the llvmjit BuildRequires) while
+# C is compiled by gcc; with SUSE's default -flto=auto the mixed toolchain
+# produces archives/objects the linker cannot combine.
+BuildRequires:	gcc-c++
 %endif
 Requires:	postgresql%{pgmajorversion}-server curl openssl