build system: enable support for static analysis

Modules can now add the following snipped to their `Makefile`:

    MODULE_SUPPORTS_STATIC_ANALYSIS := 1

When the application is then build with `make STATIC_ANALYSIS=1`, all
modules that opted in to static analysis get build with static analysis.

Makefile.base

@@ -78,6 +78,14 @@ ifneq (,$(SRCXX))
   endif
 endif
 
+# If static analysis is enabled *and* the module claims to compile fine with it,
+# add the corresponding flags
+ifeq (1,$(STATIC_ANALYSIS))
+  ifeq (1,$(MODULE_SUPPORTS_STATIC_ANALYSIS))
+    CFLAGS := $(CFLAGS_STATIC_ANALYSIS) $(CFLAGS)
+  endif
+endif
+
 compile-commands: | $(DIRS:%=COMPILE-COMMANDS--%)
 	$(file >$(BINDIR)/$(MODULE)/compile_cmds.txt,SRC: $(sort $(SRC) $(SRC_NO_LTO)))
 	$(file >>$(BINDIR)/$(MODULE)/compile_cmds.txt,SRC_NO_LTO: $(sort $(SRC_NO_LTO)))

core/Makefile

@@ -4,4 +4,7 @@ SRC := $(filter-out mbox.c msg.c msg_bus.c thread.c thread_flags.c,$(wildcard *.
 # enable submodules
 SUBMODULES := 1
 
+# this module is expected to pass static analysis
+MODULE_SUPPORTS_STATIC_ANALYSIS := 1
+
 include $(RIOTBASE)/Makefile.base

makefiles/toolchain/gnu.inc.mk

@@ -36,6 +36,9 @@ OPTIONAL_CFLAGS_BLACKLIST += -Wdocumentation -Wno-error=documentation -Wno-docum
 # We use GDB for debugging
 include $(RIOTMAKE)/tools/gdb.inc.mk
 
+# GCC's static analysis tools can be enabled using -fanalyzer
+CFLAGS_STATIC_ANALYSIS := -fanalyzer
+
 # Data address spaces starts at zero for all supported architectures. This fixes
 # compilation at least on MSP430 and AVR.
 # See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105523

makefiles/vars.inc.mk

@@ -70,6 +70,7 @@ export CXX                   # The CXX compiler to use.
 export CCAS                  # The C compiler to use for assembler files, typically the same as CC.
 export CFLAGS                # The compiler flags. Must only ever be used with `+=`.
 export CFLAGS_CPU            # CPU architecture specific compiler flags
+export CFLAGS_STATIC_ANALYSIS# Additional CFLAGS to use when static analysis should be enabled
 export CXXUWFLAGS            # (Patterns of) flags in CFLAGS that should not be passed to CXX.
 export CXXEXFLAGS            # Additional flags that should be passed to CXX.
 export CCASUWFLAGS           # (Patterns of) flags in CFLAGS that should not be passed to CCAS.