Install musl headers directly into /after/include.

sysa/tcc-0.9.27/checksums/tcc-musl-pass3

@@ -1,2 +1,2 @@
-f8023d637f64e1e739b5f381a000eafb0f2e500dc7967ebd90642d4a13c755f8  /after/bin/tcc-musl
+fd8fdc967f227f3a8ef4f51226ac8a45b6be78eb0b127d2cdf0a9df0e19451b0  /after/bin/tcc-musl
 a650b13efc65073fb851e9db89728089d8845c401f85faaa09801874ab058089  /after/lib/tcc/libtcc1.a

sysa/tcc-0.9.27/tcc-musl-pass3.sh

@@ -14,7 +14,7 @@ src_prepare() {
 src_compile() {
     export prefix=/after
     export libdir=${prefix}/lib/musl
-    export incdir=${prefix}/include/musl
+    export incdir=${prefix}/include
     export bindir=${prefix}/bin
 
     mkdir -p ${libdir}/tcc
@@ -34,6 +34,7 @@ src_compile() {
         -D CONFIG_USE_LIBGCC=1 \
         -D TCC_VERSION=\"0.9.27\" \
         -D ONE_SOURCE=1 \
+        -I ${incdir} \
         tcc.c
 
     # libtcc1.a