runtime: print error if mmap fails

Fixes #49687

Change-Id: Ife7f64f4c98449eaff7327e09bc1fb67acee72c9
Reviewed-on: https://go-review.googlesource.com/c/go/+/379354
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

Author: ianlancetaylor

src/runtime/mem_aix.go

@@ -72,6 +72,7 @@ func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
 		throw("runtime: out of memory")
 	}
 	if err != 0 {
+		print("runtime: mprotect(", v, ", ", n, ") returned ", err, "\n")
 		throw("runtime: cannot map pages in arena address space")
 	}
 }

src/runtime/mem_bsd.go

@@ -73,6 +73,7 @@ func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
 		throw("runtime: out of memory")
 	}
 	if p != v || err != 0 {
+		print("runtime: mmap(", v, ", ", n, ") returned ", p, ", ", err, "\n")
 		throw("runtime: cannot map pages in arena address space")
 	}
 }

src/runtime/mem_darwin.go

@@ -66,6 +66,7 @@ func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
 		throw("runtime: out of memory")
 	}
 	if p != v || err != 0 {
+		print("runtime: mmap(", v, ", ", n, ") returned ", p, ", ", err, "\n")
 		throw("runtime: cannot map pages in arena address space")
 	}
 }

src/runtime/mem_linux.go

@@ -189,6 +189,7 @@ func sysMap(v unsafe.Pointer, n uintptr, sysStat *sysMemStat) {
 		throw("runtime: out of memory")
 	}
 	if p != v || err != 0 {
+		print("runtime: mmap(", v, ", ", n, ") returned ", p, ", ", err, "\n")
 		throw("runtime: cannot map pages in arena address space")
 	}
 }