add MAP_SYNC and MAP_SHARED_VALIDATE from linux v4.15

for synchronous page faults, new in linux commit
1c9725974074a047f6080eecc62c50a8e840d050 and
b6fb293f2497a9841d94f6b57bd2bb2cd222da43
note that only targets that use asm-generic/mman.h have this new
flag defined, so undef it on other targets (mips*, powerpc*).

arch/mips/bits/mman.h

@@ -18,6 +18,7 @@
 #define MAP_STACK      0x40000
 #undef MAP_HUGETLB
 #define MAP_HUGETLB    0x80000
+#undef MAP_SYNC
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 #undef MADV_SOFT_OFFLINE

arch/mips64/bits/mman.h

@@ -18,6 +18,7 @@
 #define MAP_STACK      0x40000
 #undef MAP_HUGETLB
 #define MAP_HUGETLB    0x80000
+#undef MAP_SYNC
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 #undef MADV_SOFT_OFFLINE

arch/mipsn32/bits/mman.h

@@ -18,6 +18,7 @@
 #define MAP_STACK      0x40000
 #undef MAP_HUGETLB
 #define MAP_HUGETLB    0x80000
+#undef MAP_SYNC
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 #undef MADV_SOFT_OFFLINE

arch/powerpc/bits/mman.h

@@ -4,6 +4,7 @@
 #define MAP_NORESERVE   0x40
 #undef MAP_LOCKED
 #define MAP_LOCKED	0x80
+#undef MAP_SYNC
 
 #undef MCL_CURRENT
 #define MCL_CURRENT     0x2000

arch/powerpc64/bits/mman.h

@@ -4,6 +4,7 @@
 #define MAP_NORESERVE   0x40
 #undef MAP_LOCKED
 #define MAP_LOCKED	0x80
+#undef MAP_SYNC
 
 #undef MCL_CURRENT
 #define MCL_CURRENT     0x2000

include/sys/mman.h

@@ -20,6 +20,7 @@ extern "C" {
 
 #define MAP_SHARED     0x01
 #define MAP_PRIVATE    0x02
+#define MAP_SHARED_VALIDATE 0x03
 #define MAP_TYPE       0x0f
 #define MAP_FIXED      0x10
 #define MAP_ANON       0x20
@@ -33,6 +34,7 @@ extern "C" {
 #define MAP_NONBLOCK   0x10000
 #define MAP_STACK      0x20000
 #define MAP_HUGETLB    0x40000
+#define MAP_SYNC       0x80000
 #define MAP_FILE       0
 
 #define MAP_HUGE_SHIFT 26