Drop C++11 requirement

Since we get that from all R versions we support

DESCRIPTION

@@ -12,14 +12,14 @@ Description: Provides type-stable rolling window functions over any R data
 License: MIT + file LICENSE
 URL: https://github.com/r-lib/slider, https://slider.r-lib.org
 BugReports: https://github.com/r-lib/slider/issues
-Depends: 
+Depends:
     R (>= 3.6.0)
 Imports:
     cli (>= 3.6.1),
     rlang (>= 1.1.1),
     vctrs (>= 0.6.3),
     warp
-Suggests: 
+Suggests:
     covr,
     dplyr (>= 1.0.0),
     knitr,
@@ -28,15 +28,14 @@ Suggests:
     testthat (>= 3.0.0)
 LinkingTo:
     vctrs (>= 0.6.3)
-VignetteBuilder: 
+VignetteBuilder:
     knitr
 Config/Needs/website: tidyverse/tidytemplate
 Config/testthat/edition: 3
 Encoding: UTF-8
 Roxygen: list(markdown = TRUE)
 RoxygenNote: 7.2.3
-SystemRequirements: C++11
-Collate: 
+Collate:
     'arithmetic.R'
     'block.R'
     'conditions.R'

src/summary-core-align.cpp

@@ -4,7 +4,8 @@ extern "C" {
 
 /*
  * `alignof()` is C++11 specific, so this single compilation unit requires
- * C++11, and we call these helpers from C in `summary-core.h`.
+ * C++11 (which is guaranteed by recent R versions now), and we call these
+ * helpers from C in `summary-core.h`.
  *
  * Technically `alignof()` is also in C11, but it is unclear how well R supports
  * that.