clang-format: Minor tweaks

Invert KeepEmptyLinesAtTheStartOfBlocks.  We used to require an empty
line at the beginning of functions with no local variables, which I
believe is the reason for this setting.  Now it is discouraged in new
code.

Tell clang-format to align consecutive macros, since we tend to do that.
clang-format's output isn't quite what we want here.  Typically we have
a tab after a #define for some reason, and clang-format doesn't appear
to have an option for that.  clang-format will also use a mix of tabs
and spaces to minimize indentation, which is also against our
convention.  However, the result looks better with this setting than
without.

Reviewed by:	emaste
MFC after:	2 weeks
Differential Revision:	https://reviews.freebsd.org/D29870

(cherry picked from commit 2c18289b72)

.clang-format

@@ -2,6 +2,7 @@
 ---
 BasedOnStyle: WebKit
 AlignAfterOpenBracket: DontAlign
+AlignConsecutiveMacros: AcrossEmptyLines
 AlignConsecutiveAssignments: false
 AlignConsecutiveDeclarations: false
 AlignEscapedNewlines: Left
@@ -94,6 +95,7 @@ ForEachMacros:
   - TAILQ_FOREACH_SAFE
   - VM_MAP_ENTRY_FOREACH
   - VM_PAGE_DUMP_FOREACH
+SpaceBeforeParens: ControlStatementsExceptForEachMacros
 IndentCaseLabels: false
 IndentPPDirectives: None
 Language: Cpp
@@ -162,7 +164,7 @@ IncludeCategories:
 # http://llvm.org/docs/CodingStandards.html#include-style
 IncludeIsMainRegex: 'BLAH_DONT_MATCH_ANYTHING'
 SortIncludes: true
-KeepEmptyLinesAtTheStartOfBlocks: true
+KeepEmptyLinesAtTheStartOfBlocks: false
 TypenameMacros:
   - ARB_ELMTYPE
   - ARB_HEAD