SERVER-40160 Remove `if_constexpr.h` header.

This header circumvented bad formatting which `clang-format-3.8`
imparted to `if constexpr`.  Now `clang-format-7.0.1` imparts
a reasonable format to `if constexpr` so this header is not
needed anymore.

2 files changed, 2 insertions, 5 deletions

diff --git a/src/mongo/base/parse_number_test.cpp b/src/mongo/base/parse_number_test.cpp
index 577f2c3b38d..dff4e2fc9f6 100644
--- a/src/mongo/base/parse_number_test.cpp
+++ b/src/mongo/base/parse_number_test.cpp
@@ -39,7 +39,6 @@
 #include "mongo/base/parse_number.h"
 #include "mongo/base/status.h"
 #include "mongo/unittest/unittest.h"
-#include "mongo/util/if_constexpr.h"
 #include "mongo/util/str.h"  // for str::stream()!
 
 #define ASSERT_PARSES_WITH_PARSER(type, input_string, parser, expected_value) \
diff --git a/src/mongo/base/unwind_test.cpp b/src/mongo/base/unwind_test.cpp
index 7b2e5129d5f..292c20076a4 100644
--- a/src/mongo/base/unwind_test.cpp
+++ b/src/mongo/base/unwind_test.cpp
@@ -42,7 +42,6 @@
 
 #include "mongo/base/backtrace_visibility_test.h"
 #include "mongo/unittest/unittest.h"
-#include "mongo/util/if_constexpr.h"
 #include "mongo/util/stacktrace.h"
 
 namespace mongo {
@@ -98,10 +97,9 @@ struct Context {
 // Disable clang-format for the "if constexpr"
 template <int N>
 void callNext(Context& ctx) {
-    IF_CONSTEXPR(N == 0) {
+    if constexpr (N == 0) {
         ctx.s = trace();
-    }
-    else {
+    } else {
         ctx.plan[N - 1](ctx);
     }