Build with LTO

Resolves: rhbz#2188418

clang.spec

@@ -45,7 +45,7 @@
 
 Name:		%pkg_name
 Version:	%{clang_version}%{?rc_ver:~rc%{rc_ver}}
-Release:	3%{?dist}
+Release:	4%{?dist}
 Summary:	A C language family front-end for LLVM
 
 License:	Apache-2.0 WITH LLVM-exception OR NCSA
@@ -324,14 +324,17 @@ rm test/CodeGen/profile-filter.c
 
 %build
 
-%define _lto_cflags %{nil}
-
 %if 0%{?__isa_bits} == 64
 sed -i 's/\@FEDORA_LLVM_LIB_SUFFIX\@/64/g' test/lit.cfg.py
 %else
 sed -i 's/\@FEDORA_LLVM_LIB_SUFFIX\@//g' test/lit.cfg.py
 %endif
 
+%ifarch %ix86
+# Linking libclang.so goes out of memory even with ThinLTO and a single link job.
+%global _lto_cflags %nil
+%endif
+
 %ifarch s390 s390x %{arm} aarch64 %ix86 ppc64le
 # Decrease debuginfo verbosity to reduce memory consumption during final library linking
 %global optflags %(echo %{optflags} | sed 's/-g /-g1 /')
@@ -350,6 +353,9 @@ mv ../cmake-%{compat_ver}.src ../cmake
 
 %global targets_to_build "X86;AMDGPU;PowerPC;NVPTX;SystemZ;AArch64;ARM;Mips;BPF;WebAssembly"
 
+# Disable LTO when building the compat libraries. This would perform LTO across all of LLVM and
+# Clang, and fails due to "too many open files". We don't particularly care about the performance
+# of these compat libraries.
 %cmake -S ../llvm-%{compat_ver}.src -B ../clang-compat-libs -G Ninja \
 	-DLLVM_ENABLE_PROJECTS=clang \
 	-DCMAKE_BUILD_TYPE=Release \
@@ -358,7 +364,9 @@ mv ../cmake-%{compat_ver}.src ../cmake
 	-DLLVM_ENABLE_RTTI:BOOL=ON \
 	-DCMAKE_SKIP_RPATH:BOOL=ON \
 	-DLLVM_TARGETS_TO_BUILD=%{targets_to_build} \
-	-DLLVM_INCLUDE_BENCHMARKS=OFF
+	-DLLVM_INCLUDE_BENCHMARKS=OFF \
+	-DCMAKE_C_FLAGS_RELEASE="-fno-lto" \
+	-DCMAKE_CXX_FLAGS_RELEASE="-fno-lto"
 
 %ninja_build -C ../clang-compat-libs libclang.so
 %ninja_build -C ../clang-compat-libs libclang-cpp.so
@@ -678,6 +686,9 @@ mv ./libclang-cpp.so.%{compat_maj_ver} "$compat_lib"
 
 %endif
 %changelog
+* Fri Jun 02 2023 Nikita Popov <npopov@redhat.com> - 16.0.1-4
+- Build with LTO
+
 * Thu May 25 2023 Nikita Popov <npopov@redhat.com> - 16.0.1-3
 - Use ld from gcc-toolset