unix/linux: enable binding generation for ppc architecture

The remaining system call bindings for linux/ppc should be generated
by mkall.sh.

Add ppc to the target architecture list in mkall.go.  Update the
Dockerfile to install the required cross-compiler for ppc.

unix/linux/Dockerfile

@@ -45,8 +45,8 @@ RUN apt-get update && apt-get install -y \
         gcc-aarch64-linux-gnu       gcc-arm-linux-gnueabi     \
         gcc-mips-linux-gnu          gcc-mips64-linux-gnuabi64 \
         gcc-mips64el-linux-gnuabi64 gcc-mipsel-linux-gnu      \
-        gcc-powerpc64-linux-gnu     gcc-powerpc64le-linux-gnu \
-	gcc-riscv64-linux-gnu                                 \
+        gcc-powerpc-linux-gnu       gcc-powerpc64-linux-gnu   \
+        gcc-powerpc64le-linux-gnu   gcc-riscv64-linux-gnu     \
         gcc-s390x-linux-gnu         gcc-sparc64-linux-gnu     \
     && apt-get clean \
     && rm -rf /var/lib/apt/lists/*

unix/linux/mkall.go

@@ -107,6 +107,13 @@ var targets = []target{
 		GNUArch:   "mips64el-linux-gnuabi64",
 		Bits:      64,
 	},
+	{
+		GoArch:    "ppc",
+		LinuxArch: "powerpc",
+		GNUArch:   "powerpc-linux-gnu",
+		BigEndian: true,
+		Bits:      32,
+	},
 	{
 		GoArch:    "ppc64",
 		LinuxArch: "powerpc",