Build and documentation fixes for FreeBSD

We rely on thin archives via `ar rcT` for libcprover-cpp nests archives, which
FreeBSD's `ar` does not support. Use `llvm-ar` instead, which does have this
capability. This enables a successful build.

COMPILING.md

@@ -16,7 +16,7 @@ The environments below have been used successfully in the
 past, but are not actively tested:
 
 - Solaris 11
-- FreeBSD 11
+- FreeBSD 13
 
 # Building using CMake
 
@@ -246,11 +246,11 @@ Maven 3 manually.
 
 1. As root, get the necessary tools:
    ```
-   pkg install bash gmake git www/p5-libwww patch flex bison
+   pkg install bash gmake git www/p5-libwww python python3 patch flex bison cvc5 z3
    ```
    To compile JBMC, additionally install
    ```
-   pkg install openjdk8 wget maven3
+   pkg install openjdk8 wget maven
    ```
 2. As a user, get the CBMC source via
    ```

src/common

@@ -64,7 +64,7 @@ ifeq ($(filter-out OSX OSX_Universal,$(BUILD_ENV_)),)
   YFLAGS ?= -v
 else ifeq ($(filter-out FreeBSD,$(BUILD_ENV_)),)
   CP_CXXFLAGS +=
-  LINKLIB = ar rcT $@ $^
+  LINKLIB = llvm-ar rcT $@ $^
   LINKBIN = $(CXX) $(LINKFLAGS) -o $@ -Wl,--start-group $^ -Wl,--end-group $(LIBS)
   LINKNATIVE = $(HOSTCXX) $(HOSTLINKFLAGS) -o $@ $^
   ifeq ($(origin CC),default)