[openwrt/openwrt] scripts: ext-toolchain: add support for musl

[LEDE Commits]

hauke pushed a commit to openwrt/openwrt.git, branch openwrt-22.03:
https://git.openwrt.org/4ad6925a9e6685ecb1931cd76431d1339f47e8c2

commit 4ad6925a9e6685ecb1931cd76431d1339f47e8c2
Author: Christian Marangi <ansuelsmth at gmail.com>
AuthorDate: Sun Jul 17 17:56:59 2022 +0200

    scripts: ext-toolchain: add support for musl
    
    Openwrt now supports only glibc and musl. Add support for musl and
    rework the libc check to handle the new config flags and correctly
    compile package basend on that.
    
    Signed-off-by: Christian Marangi <ansuelsmth at gmail.com>
    (cherry picked from commit 7be01fe13b4517e5edb8a4818f437d60144cdcb4)
---
 scripts/ext-toolchain.sh | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/scripts/ext-toolchain.sh b/scripts/ext-toolchain.sh
index 1f8eca3076..fe1024c18e 100755
--- a/scripts/ext-toolchain.sh
+++ b/scripts/ext-toolchain.sh
@@ -369,8 +369,18 @@ print_config() {
 	echo "CONFIG_TOOLCHAIN_PREFIX=\"$prefix\"" >> "$config"
 	echo "CONFIG_TARGET_NAME=\"$target\"" >> "$config"
 
-	if [ "$LIBC_TYPE" != glibc ]; then
-		echo "CONFIG_TOOLCHAIN_LIBC=\"$LIBC_TYPE\"" >> "$config"
+	if [ -f "$config" ]; then
+		sed -i '/CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_MUSL/d' "$config"
+		sed -i '/CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_GLIBC/d' "$config"
+	fi
+
+	if [ "$LIBC_TYPE" == glibc ]; then
+		echo "CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_GLIBC=y" >> "$config"
+	elif [ "$LIBC_TYPE" == musl ]; then
+		echo "CONFIG_EXTERNAL_TOOLCHAIN_LIBC_USE_MUSL=y" >> "$config"
+	else
+		echo "Can't detect LIBC type. Aborting!" >&2
+		return 1
 	fi
 
 	local lib