Fixed Alpine/musl builds, replaced QEMU with native ARM runners

- gcc-preinclude.h: include <unistd.h> with _GNU_SOURCE active to
  provide syscall() on musl (fixes GCC 13 atomic_wait.h bug); use
  __GLIBC__ instead of __USE_GNU to guard glibc symbol versioning
- CI: linux-arm64 glibc builds now use native ubuntu-24.04-arm runners
  instead of QEMU emulation (much faster)
- CI: QEMU/Docker retained only for Alpine/musl builds (renamed to
  build-musl)

Author: jonatansberg

.github/workflows/ci.yml

@@ -48,6 +48,18 @@ jobs:
             node: 24
             host: arm64
             target: arm64
+          - os: ubuntu-24.04-arm
+            node: 20
+            host: arm64
+            target: arm64
+          - os: ubuntu-24.04-arm
+            node: 22
+            host: arm64
+            target: arm64
+          - os: ubuntu-24.04-arm
+            node: 24
+            host: arm64
+            target: arm64
     name: ${{ matrix.os }} (node=${{ matrix.node }}, host=${{ matrix.host }}, target=${{ matrix.target }})
     steps:
       - uses: actions/checkout@v6
@@ -112,8 +124,8 @@ jobs:
         run: yarn upload --upload-all ${{ github.token }}
         if: matrix.node == 24 && startsWith(github.ref, 'refs/tags/')
 
-  build-qemu:
-    runs-on: ubuntu-latest
+  build-musl:
+    runs-on: ubuntu-24.04-arm
     if: github.event_name == 'workflow_dispatch' || startsWith(github.ref, 'refs/tags/')
     strategy:
       fail-fast: false
@@ -122,15 +134,10 @@ jobs:
           - 24
         target:
           - linux/arm64
+          - linux/amd64
         variant:
-          - bookworm
           - alpine3.20
-        include:
-          # musl x64 builds
-          - target: linux/amd64
-            variant: alpine3.20
-            node: 24
-    name: ${{ matrix.variant }} (node=${{ matrix.node }}, target=${{ matrix.target }})
+    name: musl ${{ matrix.target == 'linux/arm64' && 'arm64' || 'amd64' }} (node=${{ matrix.node }})
     steps:
       - uses: actions/checkout@v6
 
@@ -158,7 +165,7 @@ jobs:
         uses: actions/upload-artifact@v7
         if: matrix.node == 24
         with:
-          name: prebuilt-binaries-${{ matrix.variant }}-${{ matrix.target == 'linux/arm64' && 'linux-arm64' || 'linux-amd64' }}
+          name: prebuilt-binaries-musl-${{ matrix.target == 'linux/arm64' && 'arm64' || 'amd64' }}
           path: prebuilds/*
           retention-days: 7
 

src/gcc-preinclude.h

@@ -4,9 +4,10 @@
 
 #define _GNU_SOURCE
 #include <features.h>
+#include <unistd.h>
 #undef _GNU_SOURCE
 
-#if defined(__USE_GNU)
+#if defined(__GLIBC__)
 
 #if defined(__x86_64__)
 __asm__(".symver memcpy,memcpy@GLIBC_2.2.5");