Upstream (JUCE, bundled): https://github.com/juce-framework/JUCE/pull/1239

From 393de14d3fb55e462eeae24a4e64978a8a30cd4f Mon Sep 17 00:00:00 2001
From: Violet Purcell <vimproved@inventati.org>
Date: Thu, 15 Jun 2023 19:01:32 +0000
Subject: [PATCH] JUCE: Add support for musl

---
 JUCE/modules/juce_core/juce_core.cpp          |  2 +-
 .../native/juce_linux_SystemStats.cpp         | 34 +++++++++++++++++--
 .../juce_core/native/juce_posix_SharedCode.h  |  2 +-
 .../juce_core/system/juce_SystemStats.cpp     |  2 +-
 .../juce_core/system/juce_TargetPlatform.h    |  9 +++++
 5 files changed, 43 insertions(+), 6 deletions(-)

diff --git a/JUCE/modules/juce_core/juce_core.cpp b/JUCE/modules/juce_core/juce_core.cpp
index 9f87047..c6f28ce 100644
--- a/JUCE/modules/juce_core/juce_core.cpp
+++ b/JUCE/modules/juce_core/juce_core.cpp
@@ -93,7 +93,7 @@
  #include <net/if.h>
  #include <sys/ioctl.h>
 
- #if ! JUCE_ANDROID
+ #if ! (JUCE_ANDROID || JUCE_MUSL)
   #include <execinfo.h>
  #endif
 #endif
diff --git a/JUCE/modules/juce_core/native/juce_linux_SystemStats.cpp b/JUCE/modules/juce_core/native/juce_linux_SystemStats.cpp
index 4b8f4bd..55906eb 100644
--- a/JUCE/modules/juce_core/native/juce_linux_SystemStats.cpp
+++ b/JUCE/modules/juce_core/native/juce_linux_SystemStats.cpp
@@ -126,9 +126,37 @@ static String getLocaleValue (nl_item key)
     return result;
 }
 
-String SystemStats::getUserLanguage()    { return getLocaleValue (_NL_IDENTIFICATION_LANGUAGE); }
-String SystemStats::getUserRegion()      { return getLocaleValue (_NL_IDENTIFICATION_TERRITORY); }
-String SystemStats::getDisplayLanguage() { return getUserLanguage() + "-" + getUserRegion(); }
+String SystemStats::getUserLanguage()
+{
+   #if JUCE_GLIBC
+    return getLocaleValue (_NL_ADDRESS_LANG_AB);
+   #else
+    if (auto langEnv = getenv ("LANG"))
+        return String::fromUTF8 (langEnv).upToLastOccurrenceOf (".UTF-8", false, true);
+
+    return {};
+   #endif
+}
+
+String SystemStats::getUserRegion()
+{
+   #if JUCE_GLIBC
+    return getLocaleValue (_NL_ADDRESS_COUNTRY_AB2);
+   #else
+    return {};
+   #endif
+}
+
+String SystemStats::getDisplayLanguage()
+{
+    auto result = getUserLanguage();
+    auto region = getUserRegion();
+
+    if (region.isNotEmpty())
+        result << "-" << region;
+
+    return result;
+}
 
 //==============================================================================
 void CPUInformation::initialise() noexcept
diff --git a/JUCE/modules/juce_core/native/juce_posix_SharedCode.h b/JUCE/modules/juce_core/native/juce_posix_SharedCode.h
index 876e681..59c49ba 100644
--- a/JUCE/modules/juce_core/native/juce_posix_SharedCode.h
+++ b/JUCE/modules/juce_core/native/juce_posix_SharedCode.h
@@ -235,7 +235,7 @@ int juce_siginterrupt (int sig, int flag)
 //==============================================================================
 namespace
 {
-   #if JUCE_LINUX || (JUCE_IOS && ! __DARWIN_ONLY_64_BIT_INO_T) // (this iOS stuff is to avoid a simulator bug)
+   #if JUCE_GLIBC || (JUCE_IOS && ! __DARWIN_ONLY_64_BIT_INO_T) // (this iOS stuff is to avoid a simulator bug)
     typedef struct stat64 juce_statStruct;
     #define JUCE_STAT     stat64
    #else
diff --git a/JUCE/modules/juce_core/system/juce_SystemStats.cpp b/JUCE/modules/juce_core/system/juce_SystemStats.cpp
index 7e05277..cac9a14 100644
--- a/JUCE/modules/juce_core/system/juce_SystemStats.cpp
+++ b/JUCE/modules/juce_core/system/juce_SystemStats.cpp
@@ -120,7 +120,7 @@ String SystemStats::getStackBacktrace()
 {
     String result;
 
-   #if JUCE_ANDROID || JUCE_MINGW
+   #if JUCE_ANDROID || JUCE_MINGW || JUCE_MUSL
     jassertfalse; // sorry, not implemented yet!
 
    #elif JUCE_WINDOWS
diff --git a/JUCE/modules/juce_core/system/juce_TargetPlatform.h b/JUCE/modules/juce_core/system/juce_TargetPlatform.h
index ae9d7e1..9dca4bc 100644
--- a/JUCE/modules/juce_core/system/juce_TargetPlatform.h
+++ b/JUCE/modules/juce_core/system/juce_TargetPlatform.h
@@ -33,6 +33,7 @@
     - Either JUCE_LITTLE_ENDIAN or JUCE_BIG_ENDIAN.
     - Either JUCE_INTEL or JUCE_ARM
     - Either JUCE_GCC or JUCE_CLANG or JUCE_MSVC
+    - Either JUCE_GLIBC or JUCE_MUSL will be defined on Linux depending on the system's libc implementation.
 */
 
 //==============================================================================
@@ -177,6 +178,14 @@
   #elif __MMX__ || __SSE__ || __amd64__
     #define JUCE_INTEL 1
   #endif
+
+  #if JUCE_LINUX
+    #ifdef __GLIBC__
+      #define JUCE_GLIBC 1
+    #else
+      #define JUCE_MUSL 1
+    #endif
+  #endif
 #endif
 
 //==============================================================================
-- 
2.41.0