travis: add x86 musl

* .travis.yml (matric): Add musl-gcc/x86.
* travis-build.sh [TARGET == x86]: Specify --target along with --build
to configure.
* travis-install.sh [CC == musl-gcc && TARGET == x32]: Add -mx32 to $CC.
[CC == musl-gcc && TARGET == x86]: Add -m32 to $CC.  Specify --build
and --target to musl configure invocation.

.travis.yml

@@ -39,3 +39,6 @@ matrix:
     - compiler: clang-3.6
       env:
         - TARGET=x86
+    - compiler: musl-gcc
+      env:
+        - TARGET=x86

travis-build.sh

@@ -17,7 +17,7 @@ case "${TARGET-}" in
 		;;
 	x86)
 		CC="$CC -m32"
-		export DISTCHECK_CONFIGURE_FLAGS='--build=i686-pc-linux-gnu'
+		export DISTCHECK_CONFIGURE_FLAGS='--build=i686-pc-linux-gnu --target=i686-pc-linux-gnu'
 		;;
 esac
 

travis-install.sh

@@ -23,7 +23,17 @@ case "$CC" in
 		git clone --depth=1 https://github.com/strace/musl
 		cd musl
 			CC=gcc
-			./configure --prefix=/opt/musl --exec-prefix=/usr
+			build=
+			case "${TARGET-}" in
+				x32)
+					CC="$CC -mx32"
+					;;
+				x86)
+					CC="$CC -m32"
+					build='--build=i686-pc-linux-gnu --target=i686-pc-linux-gnu'
+					;;
+			esac
+			./configure --prefix=/opt/musl --exec-prefix=/usr ${build}
 			make
 			sudo make install
 		cd -