GCN, nvptx: Allow for "hosted" libstdc++ build

We need '-fno-exceptions', '-fno-rtti', disable generation of PCH files, and
for nvptx twiddle some more knobs.

	PR target/92713
	PR target/101544
	libstdc++-v3/
	* config/cpu/nvptx/cpu_defines.h: New.
	* config/cpu/nvptx/t-nvptx: Likewise.
	* configure.host: Handle GCN, nvptx.

(cherry picked from commit 1268924a2e)

libstdc++-v3/ChangeLog.omp

@@ -1,5 +1,14 @@
 2025-03-19  Thomas Schwinge  <tschwinge@baylibre.com>
 
+	Backported from trunk:
+	2025-03-14  Thomas Schwinge  <tschwinge@baylibre.com>
+
+	PR target/92713
+	PR target/101544
+	* config/cpu/nvptx/cpu_defines.h: New.
+	* config/cpu/nvptx/t-nvptx: Likewise.
+	* configure.host: Handle GCN, nvptx.
+
 	Backported from trunk:
 	2025-03-13  Thomas Schwinge  <tschwinge@baylibre.com>
 

libstdc++-v3/config/cpu/nvptx/cpu_defines.h

@@ -0,0 +1,36 @@
+// Specific definitions for nvptx platforms  -*- C++ -*-
+
+// Copyright (C) 2025 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file bits/cpu_defines.h
+ *  This is an internal header file, included by other library headers.
+ *  Do not attempt to use it directly. @headername{iosfwd}
+ */
+
+#ifndef _GLIBCXX_CPU_DEFINES
+#define _GLIBCXX_CPU_DEFINES 1
+
+// No support for referencing weak symbols without a definition.
+#define _GLIBCXX_USE_WEAK_REF 0
+
+#endif

libstdc++-v3/config/cpu/nvptx/t-nvptx

@@ -0,0 +1,7 @@
+# Per-file flags, see '../../../configure.host', "inject per-file flags".
+
+# 'ptxas'/CUDA Driver rejects objects with a lot of global constant data:
+#     ptxas error   : File uses too much global constant data ([...])
+# Cut short the assembly-time check; defer to actual use of the object file.
+AM_MAKEFLAGS += CXXFLAGS-src/c++17/floating_to_chars.lo=-Wa,--no-verify
+AM_MAKEFLAGS += CXXFLAGS-src/c++20/tzdb.lo=-Wa,--no-verify

libstdc++-v3/configure.host

@@ -150,6 +150,9 @@ case "${host_cpu}" in
   arm*)
     cpu_defines_dir=cpu/arm
     ;;
+  nvptx)
+    cpu_defines_dir=cpu/nvptx
+    ;;
   powerpc* | rs6000)
     cpu_defines_dir=cpu/powerpc
     ;;
@@ -367,6 +370,16 @@ case "${host}" in
   arm*-*-freebsd*)
      port_specific_symbol_files="\$(srcdir)/../config/os/gnu-linux/arm-eabi-extra.ver"
      ;;
+  nvptx-*-none)
+    # For 'make all-target-libstdc++-v3', we need to inject per-file flags:
+    OPTIMIZE_CXXFLAGS="${OPTIMIZE_CXXFLAGS} \$(CXXFLAGS-\$(subdir)/\$@)"
+    # ..., see:
+    tmake_file="$tmake_file cpu/nvptx/t-nvptx"
+
+    # For 'make all-target-libstdc++-v3', re 'alloca'/VLA usage:
+    EXTRA_CFLAGS="${EXTRA_CFLAGS} -mfake-ptx-alloca"
+    OPTIMIZE_CXXFLAGS="${OPTIMIZE_CXXFLAGS} -mfake-ptx-alloca"
+    ;;
   powerpc*-*-darwin*)
     port_specific_symbol_files="\$(srcdir)/../config/os/bsd/darwin/ppc-extra.ver"
     ;;
@@ -383,3 +396,27 @@ case "${host}" in
     abi_baseline_subdir_switch=--print-multi-os-directory
     ;;
 esac
+
+
+# Dumb down libstdc++ for certain configurations.
+# THIS TABLE IS SORTED.  KEEP IT THAT WAY.
+case "${host}" in
+  amdgcn-*-amdhsa \
+  | nvptx-*-none )
+    # For 'make all-target-libstdc++-v3' and 'make check-target-libstdc++-v3',
+    # exception handling is not supported: in case that exception handling
+    # constructs survive compiler optimizations, the back ends error out:
+    #     sorry, unimplemented: exception handling not supported
+    EXTRA_CXX_FLAGS="${EXTRA_CXX_FLAGS} -fno-exceptions"
+
+    # For 'make all-target-libstdc++-v3' and 'make check-target-libstdc++-v3',
+    # RTTI is not supported.
+    EXTRA_CXX_FLAGS="${EXTRA_CXX_FLAGS} -fno-rtti"
+
+    # Cannot '#include' all newlib header files without explosion, for example:
+    #     error: 'jmp_buf' was not declared in this scope
+    # Just disable generation of PCH files here, instead of attempting to care
+    # for such special cases in some more complex way.
+    enable_libstdcxx_pch=no
+    ;;
+esac