Define os_posix in gyp files to get new Unix platforms added quickly

base/allocator/allocator.gyp

Index: base/allocator/allocator.gyp
diff --git a/base/allocator/allocator.gyp b/base/allocator/allocator.gyp
index 065cbf4b711f78d4e4745b3123bb87c40b289898..1e9617199654115ffc775757cea69e967e63351c 100644
--- a/base/allocator/allocator.gyp
+++ b/base/allocator/allocator.gyp
@@ -309,7 +309,7 @@
             '<(tcmalloc_dir)/src/debugallocation.cc',
           ],
         }],
-        ['OS=="linux" or OS=="freebsd" or OS=="openbsd"', {
+        ['OS=="linux" or OS=="freebsd" or OS=="solaris"', {
           'sources!': [
             '<(tcmalloc_dir)/src/system-alloc.h',
             '<(tcmalloc_dir)/src/windows/port.cc',