Fix for the Android x86-64 megazord with Android NDK-25

The new NDK doesn't link to `libgcc` anymore, which breaks our our NSS
and SQLCipher libraries since they depended on the symbols from
libclang_rt.builtins-x86_64-android` like `__extenddftf2`. See #5436 for
more details.

The change works around this by manually linking to the
libclang_rt.builtins-x86_64-android library in this case.

Added a doc on how to upgrade the Android NDK which hopefully will help
us in the future.  Extracted some common code from the the
`build-*-android.sh` scripts to make these directions simpler.

components/support/rc_crypto/nss/nss_build_common/src/lib.rs

@@ -89,6 +89,15 @@ fn link_nss_libs(kind: LinkingKind) {
     } else {
         println!("cargo:rustc-link-lib=c++");
     }
+    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+    if target_arch == "x86_64" && target_os == "android" {
+        let android_home = env::var("ANDROID_HOME").expect("ANDROID_HOME not set");
+        const ANDROID_NDK_VERSION: &str = "25.2.9519653";
+        const LINUX_X86_64_LIB_DIR: &str =
+            "/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/14.0.7/lib/linux/";
+        println!("cargo:rustc-link-search={android_home}/ndk/{ANDROID_NDK_VERSION}/{LINUX_X86_64_LIB_DIR}");
+        println!("cargo:rustc-link-lib=static=clang_rt.builtins-x86_64-android");
+    }
 }
 
 fn get_nss_libs(kind: LinkingKind) -> Vec<&'static str> {

docs/howtos/upgrades/android-ndk.md

@@ -0,0 +1,14 @@
+Here's how to upgrade the Android NDK version:
+
+* Update the version number in:
+  * `build.gradle` (search for `ndkVersion`)
+  * `taskcluster/docker/linux/Dockerfile` (search for `ANDROID_NDK_VERSION`)
+  * `components/support/rc_crypto/nss/nss_build_common/src/lib.rs` (search for `ANDROID_NDK_VERSION`)
+* Update these docs by replacing the old version with the new one:
+  * docs/building.md
+  * docs/howtos/locally-building-jna.md
+* These may need updating if the directory structure changed between this version and the last
+  * `libs/build-android-common.sh`: ensure the paths to the various binaries are correct.
+  * `components/support/rc_crypto/nss/nss_build_common/src/lib.rs`: search for
+    `LINUX_X86_64_LIB_DIR` and ensure this correctly points to the correct lib directory containing
+    `libclang_rt.builtins-x86_64-android.a`.

libs/build-android-common.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+# This script is sourced by the `build-*-android.sh` scripts.  The shbang above
+# is to make shellcheck happy.
+
+export AR="${TOOLCHAIN_PATH}/bin/llvm-ar"
+export CC="${TOOLCHAIN_PATH}/bin/${TOOLCHAIN}${ANDROID_NDK_API_VERSION}-clang"
+export CXX="${TOOLCHAIN_PATH}/bin/${TOOLCHAIN}${ANDROID_NDK_API_VERSION}-clang++"
+# For 32-bit ARM, the compiler is prefixed with armv7a-linux-androideabi
+if [[ "${TOOLCHAIN}" == "arm-linux-androideabi" ]]; then
+  export CC="${TOOLCHAIN_PATH}/bin/armv7a-linux-androideabi${ANDROID_NDK_API_VERSION}-clang"
+  export CXX="${TOOLCHAIN_PATH}/bin/armv7a-linux-androideabi${ANDROID_NDK_API_VERSION}-clang++"
+fi
+export LD="${TOOLCHAIN_PATH}/bin/ld"
+export NM="${TOOLCHAIN_PATH}/bin/llvm-nm"
+export RANLIB="${TOOLCHAIN_PATH}/bin/llvm-ranlib"
+export READELF="${TOOLCHAIN_PATH}/bin/llvm-readelf"
+

libs/build-nss-android.sh

@@ -42,18 +42,8 @@ else
 fi
 NSPR_64="${NSPR_64:-""}"
 
-export AR="${TOOLCHAIN_PATH}/bin/llvm-ar"
+# shellcheck source=libs/build-android-common.sh
-export CC="${TOOLCHAIN_PATH}/bin/${TOOLCHAIN}${ANDROID_NDK_API_VERSION}-clang"
+source ./build-android-common.sh
-export CXX="${TOOLCHAIN_PATH}/bin/${TOOLCHAIN}${ANDROID_NDK_API_VERSION}-clang++"
-# For 32-bit ARM, the compiler is prefixed with armv7a-linux-androideabi
-if [[ "${TOOLCHAIN}" == "arm-linux-androideabi" ]]; then
-  export CC="${TOOLCHAIN_PATH}/bin/armv7a-linux-androideabi${ANDROID_NDK_API_VERSION}-clang"
-  export CXX="${TOOLCHAIN_PATH}/bin/armv7a-linux-androideabi${ANDROID_NDK_API_VERSION}-clang++"
-fi
-export LD="${TOOLCHAIN_PATH}/bin/ld"
-export NM="${TOOLCHAIN_PATH}/bin/llvm-nm"
-export RANLIB="${TOOLCHAIN_PATH}/bin/llvm-ranlib"
-export READELF="${TOOLCHAIN_PATH}/bin/llvm-readelf"
 
 # Build NSPR
 NSPR_BUILD_DIR=$(mktemp -d)

libs/build-sqlcipher-android.sh

@@ -23,16 +23,8 @@ if [[ -d "${DIST_DIR}" ]]; then
   exit 0
 fi
 
-export AR="${TOOLCHAIN_PATH}/bin/llvm-ar"
+# shellcheck source=libs/build-android-common.sh
-export CC="${TOOLCHAIN_PATH}/bin/${TOOLCHAIN}${ANDROID_NDK_API_VERSION}-clang"
+source ./build-android-common.sh
-export CXX="${TOOLCHAIN_PATH}/bin/${TOOLCHAIN}${ANDROID_NDK_API_VERSION}-clang++"
-# For 32-bit ARM, the compiler is prefixed with armv7a-linux-androideabi
-if [[ "${TOOLCHAIN}" == "arm-linux-androideabi" ]]; then
-  export CC="${TOOLCHAIN_PATH}/bin/armv7a-linux-androideabi${ANDROID_NDK_API_VERSION}-clang"
-  export CXX="${TOOLCHAIN_PATH}/bin/armv7a-linux-androideabi${ANDROID_NDK_API_VERSION}-clang++"
-fi
-export LD="${TOOLCHAIN_PATH}/bin/ld"
-export RANLIB="${TOOLCHAIN_PATH}/bin/llvm-ranlib"
 
 if [[ "${TOOLCHAIN}" == "x86_64-linux-android" ]]
 then