os: add os.page_size() (#19770)

vlib/os/os_nix.c.v

@@ -506,3 +506,10 @@ pub fn posix_set_permission_bit(path_s string, mode u32, enable bool) {
 fn get_long_path(path string) !string {
 	return path
 }
+
+fn C.sysconf(name int) i64
+
+// page_size returns the page size in bytes.
+pub fn page_size() int {
+	return int(C.sysconf(C._SC_PAGESIZE))
+}

vlib/os/os_test.v

@@ -1012,3 +1012,7 @@ fn test_mv_by_cp_across_partitions() {
 fn test_mv_across_partitions() {
 	move_across_partitions_using_function(os.mv)!
 }
+
+fn test_page_size() {
+	assert os.page_size() >= 4096 // this is normal and assumed.
+}

vlib/os/os_windows.c.v

@@ -592,3 +592,19 @@ fn get_long_path(path string) !string {
 	long_path := unsafe { string_from_wide(&long_path_buf[0]) }
 	return long_path
 }
+
+// C.SYSTEM_INFO contains information about the current computer system. This includes the architecture and type of the processor, the number of processors in the system, the page size, and other such information.
+[typedef]
+pub struct C.SYSTEM_INFO {
+	dwNumberOfProcessors u32
+	dwPageSize           u32
+}
+
+fn C.GetSystemInfo(&C.SYSTEM_INFO)
+
+// page_size returns the page size in bytes.
+pub fn page_size() int {
+	sinfo := C.SYSTEM_INFO{}
+	C.GetSystemInfo(&sinfo)
+	return int(sinfo.dwPageSize)
+}

vlib/runtime/runtime_windows.c.v

@@ -2,11 +2,6 @@ module runtime
 
 import os
 
-[typedef]
-pub struct C.SYSTEM_INFO {
-	dwNumberOfProcessors u32
-}
-
 [typedef]
 pub struct C.MEMORYSTATUS {
 	dwTotalPhys usize