add more context to patches; merge fixes for stray -nostdlib++

recipe/meta.yaml

@@ -16,12 +16,10 @@ source:
       # See https://discourse.llvm.org/t/shipping-custom-libc-on-macos/58606
       - patches/0002-Fix-ABI-compatibility-with-system.patch    # [sys_abi == "pre-12"]
       - patches/0003-custom-error-message-for-old-sdk.patch
-      # fix for https://github.com/llvm/llvm-project/issues/77653
+      # disable feature that requires up-to-date libcxxabi, which we don't ship
       - patches/0005-disable-_LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPT.patch
-      # GCC's C linker does not understand -nostdlib++; needs CXX
-      - patches/0006-set-CXX-as-language-for-libunwind-to-avoid-running-i.patch
-      # something broke detection of dladdr on linux
-      - patches/0007-avoid-misdetection-of-dl-pthread-on-linux.patch
+      # work around https://github.com/llvm/llvm-project/issues/90332
+      - patches/0006-Work-around-stray-nostdlib-flags-causing-errors-with.patch
 
 build:
   number: 0

recipe/patches/0001-Support-legacy-standalone-builds.patch

@@ -1,7 +1,7 @@
 From bf0dac8954fed53dcc579ccf564dd011e11616b2 Mon Sep 17 00:00:00 2001
 From: Isuru Fernando <isuruf@gmail.com>
 Date: Tue, 18 May 2021 19:51:28 -0500
-Subject: [PATCH 1/7] Support legacy standalone builds
+Subject: [PATCH 1/5] Support legacy standalone builds
 
 ---
  libcxx/src/CMakeLists.txt | 17 +++++++++++++++++

recipe/patches/0002-Fix-ABI-compatibility-with-system.patch

@@ -1,7 +1,7 @@
 From b1113a136e91b0788e2fa28e578142e45016eae9 Mon Sep 17 00:00:00 2001
 From: Isuru Fernando <isuruf@gmail.com>
 Date: Tue, 13 Jul 2021 01:57:06 -0500
-Subject: [PATCH 2/7] Fix ABI compatibility with system
+Subject: [PATCH 2/5] Fix ABI compatibility with system
 
 ---
  libcxx/src/locale.cpp | 16 ++++++++--------

recipe/patches/0003-custom-error-message-for-old-sdk.patch

@@ -1,7 +1,7 @@
 From 7e2722ee435b20f9445be40ace0f5298126ae23c Mon Sep 17 00:00:00 2001
 From: Isuru Fernando <isuruf@gmail.com>
 Date: Wed, 29 Dec 2021 19:28:35 -0800
-Subject: [PATCH 3/7] custom error message for old sdk
+Subject: [PATCH 3/5] custom error message for old sdk
 
 Co-Authored-By: H. Vetinari <h.vetinari@gmx.com>
 ---

recipe/patches/0005-disable-_LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPT.patch

@@ -1,11 +1,22 @@
-From 5499430ec91578805ae0ca5fd5c994f29e41b01d Mon Sep 17 00:00:00 2001
+From 4744d322ef96d67b8543897b49ec8897d2633a1a Mon Sep 17 00:00:00 2001
 From: "H. Vetinari" <h.vetinari@gmx.com>
 Date: Sun, 26 May 2024 22:04:04 +1100
-Subject: [PATCH 5/7] disable _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION
+Subject: [PATCH 4/5] disable _LIBCPP_AVAILABILITY_HAS_INIT_PRIMARY_EXCEPTION
  unconditionally
 
-https://github.com/llvm/llvm-project/issues/77653
-https://github.com/llvm/llvm-project/issues/86077
+When _LIBCPP_HAS_NO_VENDOR_AVAILABILITY_ANNOTATIONS is not defined, things
+work as expected: i.e. the feature is only used on macOS that vendors LLVM>=18.
+
+Our general policy of setting `-D_LIBCPP_DISABLE_AVAILABILITY` (which causes
+the above macro to be defined) wherever newer C++ features are needed works
+fine because we ship our own libcxx. In this case however, the required symbols
+(`___cxa_init_primary_exception` etc.) is in libcxxabi, which we intentionally
+don't ship ourselves.
+
+Therefore, we must disable this feature unconditionally, at least until our
+macOS baseline is >=15.0, as we rely on the libcxxabi shipped by the system.
+
+See also https://github.com/llvm/llvm-project/issues/77653 & https://github.com/llvm/llvm-project/issues/86077
 ---
  libcxx/include/__availability | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

recipe/patches/0006-Work-around-stray-nostdlib-flags-causing-errors-with.patch

@@ -0,0 +1,53 @@
+From 6a49c1d89912796cd7ea3f4a9e3eb606ca553257 Mon Sep 17 00:00:00 2001
+From: "H. Vetinari" <h.vetinari@gmx.com>
+Date: Sun, 26 May 2024 13:01:28 +1100
+Subject: [PATCH 5/5] Work around stray `-nostdlib++` flags causing errors with
+ C compiler
+
+---
+ libunwind/cmake/config-ix.cmake | 7 +++++--
+ libunwind/src/CMakeLists.txt    | 6 ++++--
+ 2 files changed, 9 insertions(+), 4 deletions(-)
+
+diff --git a/libunwind/cmake/config-ix.cmake b/libunwind/cmake/config-ix.cmake
+index 126c872f0d48..ab9ea1d5ce01 100644
+--- a/libunwind/cmake/config-ix.cmake
++++ b/libunwind/cmake/config-ix.cmake
+@@ -120,8 +120,11 @@ if(FUCHSIA)
+   set(LIBUNWIND_HAS_DL_LIB NO)
+   set(LIBUNWIND_HAS_PTHREAD_LIB NO)
+ else()
+-  check_library_exists(dl dladdr "" LIBUNWIND_HAS_DL_LIB)
+-  check_library_exists(pthread pthread_once "" LIBUNWIND_HAS_PTHREAD_LIB)
++  # misdetected due to https://github.com/llvm/llvm-project/issues/90332
++  # check_library_exists(dl dladdr "" LIBUNWIND_HAS_DL_LIB)
++  # check_library_exists(pthread pthread_once "" LIBUNWIND_HAS_PTHREAD_LIB)
++  set(LIBUNWIND_HAS_DL_LIB YES)
++  set(LIBUNWIND_HAS_PTHREAD_LIB YES)
+ endif()
+
+ if(HAIKU)
+diff --git a/libunwind/src/CMakeLists.txt b/libunwind/src/CMakeLists.txt
+index 780430ba70ba..8f53719d4007 100644
+--- a/libunwind/src/CMakeLists.txt
++++ b/libunwind/src/CMakeLists.txt
+@@ -168,7 +168,8 @@ if (LIBUNWIND_ENABLE_SHARED)
+   set_target_properties(unwind_shared
+     PROPERTIES
+       LINK_FLAGS "${LIBUNWIND_LINK_FLAGS}"
+-      LINKER_LANGUAGE C
++      # changed from C due to https://github.com/llvm/llvm-project/issues/90332
++      LINKER_LANGUAGE CXX
+       OUTPUT_NAME "${LIBUNWIND_SHARED_OUTPUT_NAME}"
+       VERSION "1.0"
+       SOVERSION "1"
+@@ -214,7 +215,8 @@ if (LIBUNWIND_ENABLE_STATIC)
+   set_target_properties(unwind_static
+     PROPERTIES
+       LINK_FLAGS "${LIBUNWIND_LINK_FLAGS}"
+-      LINKER_LANGUAGE C
++      # changed from C due to https://github.com/llvm/llvm-project/issues/90332
++      LINKER_LANGUAGE CXX
+       OUTPUT_NAME "${LIBUNWIND_STATIC_OUTPUT_NAME}"
+   )
+