ARM: 8445/1: fix vdsomunge not to depend on glibc specific byteswap.h

If the host toolchain is not glibc based then the arm kernel build
fails with

  HOSTCC  arch/arm/vdso/vdsomunge
  arch/arm/vdso/vdsomunge.c:48:22: fatal error: byteswap.h: No such file or directory

Observed: with omap2plus_defconfig and compile on Mac OS X with arm ELF
cross-compiler.

Reason: byteswap.h is a glibc only header.

Solution: replace by private byte-swapping macros (taken from
arch/mips/boot/elf2ecoff.c and kindly improved by Russell King)

Tested to compile on Mac OS X 10.9.5 host.
Signed-off-by: NH. Nikolaus Schaller <hns@goldelico.com>
Signed-off-by: NNathan Lynch <nathan_lynch@mentor.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>

arch/arm/vdso/vdsomunge.c

@@ -45,7 +45,6 @@
  * it does.
  */
 
-#include <byteswap.h>
 #include <elf.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -59,6 +58,16 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#define swab16(x) \
+	((((x) & 0x00ff) << 8) | \
+	 (((x) & 0xff00) >> 8))
+
+#define swab32(x) \
+	((((x) & 0x000000ff) << 24) | \
+	 (((x) & 0x0000ff00) <<  8) | \
+	 (((x) & 0x00ff0000) >>  8) | \
+	 (((x) & 0xff000000) << 24))
+
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define HOST_ORDER ELFDATA2LSB
 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
@@ -104,17 +113,17 @@ static void cleanup(void)
 
 static Elf32_Word read_elf_word(Elf32_Word word, bool swap)
 {
-	return swap ? bswap_32(word) : word;
+	return swap ? swab32(word) : word;
 }
 
 static Elf32_Half read_elf_half(Elf32_Half half, bool swap)
 {
-	return swap ? bswap_16(half) : half;
+	return swap ? swab16(half) : half;
 }
 
 static void write_elf_word(Elf32_Word val, Elf32_Word *dst, bool swap)
 {
-	*dst = swap ? bswap_32(val) : val;
+	*dst = swap ? swab32(val) : val;
 }
 
 int main(int argc, char **argv)