Add unistd.h checks back to the CMake build.

getpagesize(), as well as its POSIX.2001 replacement
sysconf(_SC_PAGESIZE), is defined in <unistd.h>. On Linux and OS X,
including <sys/mman.h> is sufficient to get a definition for
getpagesize(). However, this is not true for the Android NDK. This CL
brings back the HAVE_UNISTD_H definition and its associated header
check.

This also adds a HAVE_FUNC_SYSCONF definition, which checks for the
presence of sysconf(). The definition can be used later to replace
getpagesize() with sysconf().

CMakeLists.txt

@@ -22,6 +22,7 @@ check_include_file("sys/mman.h" HAVE_SYS_MMAN_H)
 check_include_file("sys/resource.h" HAVE_SYS_RESOURCE_H)
 check_include_file("sys/time.h" HAVE_SYS_TIME_H)
 check_include_file("sys/uio.h" HAVE_SYS_UIO_H)
+check_include_file("unistd.h" HAVE_UNISTD_H)
 check_include_file("windows.h" HAVE_WINDOWS_H)
 
 include(CheckLibraryExists)
@@ -37,6 +38,7 @@ check_cxx_source_compiles(
 
 include(CheckSymbolExists)
 check_symbol_exists("mmap" "sys/mman.h" HAVE_FUNC_MMAP)
+check_symbol_exists("sysconf" "unistd.h" HAVE_FUNC_SYSCONF)
 
 find_package(GTest QUIET)
 if(GTEST_FOUND)

cmake/config.h.in

@@ -13,6 +13,9 @@
 /* Define to 1 if you have a definition for mmap() in <sys/mman.h>. */
 #cmakedefine HAVE_FUNC_MMAP 1
 
+/* Define to 1 if you have a definition for sysconf() in <unistd.h>. */
+#cmakedefine HAVE_FUNC_SYSCONF 1
+
 /* Define to 1 to use the gflags package for command-line parsing. */
 #cmakedefine HAVE_GFLAGS 1
 
@@ -46,6 +49,9 @@
 /* Define to 1 if you have the <sys/uio.h> header file. */
 #cmakedefine HAVE_SYS_UIO_H 1
 
+/* Define to 1 if you have the <unistd.h> header file. */
+#cmakedefine HAVE_UNISTD_H 1
+
 /* Define to 1 if you have the <windows.h> header file. */
 #cmakedefine HAVE_WINDOWS_H 1
 

snappy-stubs-internal.h

@@ -45,6 +45,10 @@
 #include <sys/mman.h>
 #endif
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #if defined(_MSC_VER)
 #include <intrin.h>
 #endif  // defined(_MSC_VER)